diff --git a/app/api/listings/[id]/route.ts b/app/api/listings/[id]/route.ts
index 401f224..d2c660c 100644
--- a/app/api/listings/[id]/route.ts
+++ b/app/api/listings/[id]/route.ts
@@ -7,7 +7,10 @@ import {
   updateListing,
 } from "@/services/listings/listings";
 import { ListingInput } from "@/models/Listing";
-import { uploadListingImages } from "@/lib/listing-images";
+import {
+  getValidImageFiles,
+  uploadListingImages,
+} from "@/lib/listing-images";
 import { getSession } from "@/lib/rbac";
 
 const objectIdSchema = z
@@ -34,13 +37,16 @@ const listingValidationSchema = z
   .partial()
   .strict();
 
+type ListingRouteContext = { params: Promise<{ id: string }> };
+
 /**
  * Get a listing entry by ID
  * @param id the ID of the listing to get
  * ex req: GET /listings/001 HTTP/1.1
  * @returns the listing as a JS object in a JSON response
  */
-async function GET(request: Request, { params }: { params: Promise<{ id: string }> }) {
+async function GET(request: Request, context: ListingRouteContext) {
+  const { id } = await context.params;
   const { allowed, reason } = await getSession("inventory:view");
   if (!allowed) {
     return NextResponse.json(
@@ -61,7 +67,6 @@ async function GET(request: Request, { params }: { params: Promise<{ id: string
     );
   }
 
-  const { id } = await params;
   const parsedId = objectIdSchema.safeParse(id);
   if (!parsedId.success) {
     return NextResponse.json(
@@ -74,7 +79,7 @@ async function GET(request: Request, { params }: { params: Promise<{ id: string
   }
 
   try {
-    const listing = await getListing(parsedId.data); // don't need mongo doc features
+    const listing = await getListing(parsedId.data);
     if (!listing) {
       return NextResponse.json(
         { success: false, message: "Listing not found." },
@@ -95,7 +100,8 @@ async function GET(request: Request, { params }: { params: Promise<{ id: string
  * @param id the ID of the listing to get as part of the path params
  * @returns the updated listing as a JS object in a JSON response
  */
-async function PUT(request: Request, { params }: { params: Promise<{ id: string }> }) {
+async function PUT(request: Request, context: ListingRouteContext) {
+  const { id } = await context.params;
   const { allowed, reason } = await getSession("inventory:update");
   if (!allowed) {
     return NextResponse.json(
@@ -116,7 +122,6 @@ async function PUT(request: Request, { params }: { params: Promise<{ id: string
     );
   }
 
-  const { id } = await params;
   const parsedId = objectIdSchema.safeParse(id);
   if (!parsedId.success) {
     return NextResponse.json(
@@ -129,17 +134,18 @@ async function PUT(request: Request, { params }: { params: Promise<{ id: string
   }
 
   const formData = await request.formData();
-  const updateData: Partial<ListingInput> = {
-    ...Object.fromEntries(formData.entries()),
-  };
+  const textEntries: [string, FormDataEntryValue][] = [];
+  for (const [key, value] of formData.entries()) {
+    if (key === "image" || key === "images" || key === "hazardTags") continue;
+    textEntries.push([key, value]);
+  }
+  const updateData: Partial<ListingInput> = Object.fromEntries(textEntries);
 
-  // handle array fields
   const hazardTags = formData.getAll("hazardTags");
   if (hazardTags.length > 0) {
     updateData.hazardTags = hazardTags as ListingInput["hazardTags"];
   }
 
-  // type conversions
   if (updateData.quantityAvailable !== undefined) {
     updateData.quantityAvailable = Number(updateData.quantityAvailable);
   }
@@ -157,9 +163,6 @@ async function PUT(request: Request, { params }: { params: Promise<{ id: string
     }
   }
 
-  // handle image uploads if provided
-  const imageFiles = formData.getAll("images") as File[];
-
   const parsedRequest = listingValidationSchema.safeParse(updateData);
   if (!parsedRequest.success) {
     return NextResponse.json(
@@ -172,16 +175,12 @@ async function PUT(request: Request, { params }: { params: Promise<{ id: string
   }
 
   try {
-    let imageUrls: string[] | undefined;
+    const updatePayload: Partial<ListingInput> = { ...parsedRequest.data };
+    const imageFiles = getValidImageFiles(formData);
     if (imageFiles.length > 0) {
-      imageUrls = await uploadListingImages(imageFiles);
+      updatePayload.imageUrls = await uploadListingImages(imageFiles);
     }
 
-    const updatePayload: Partial<ListingInput> = {
-      ...parsedRequest.data,
-      ...(imageUrls ? { imageUrls } : {}),
-    };
-
     const updatedListing = await updateListing(parsedId.data, updatePayload);
 
     if (!updatedListing) {
@@ -218,10 +217,8 @@ async function PUT(request: Request, { params }: { params: Promise<{ id: string
  * @param id the ID of the listing to get as part of the path params
  * @returns JSON response signaling the success of the listing deletion
  */
-async function DELETE(
-  request: Request,
-  { params }: { params: Promise<{ id: string }> }
-) {
+async function DELETE(request: Request, context: ListingRouteContext) {
+  const { id } = await context.params;
   const { allowed, reason } = await getSession("inventory:delete");
   if (!allowed) {
     return NextResponse.json(
@@ -242,7 +239,6 @@ async function DELETE(
     );
   }
 
-  const { id } = await params;
   const parsedId = objectIdSchema.safeParse(id);
   if (!parsedId.success) {
     return NextResponse.json(
diff --git a/app/api/listings/__tests__/route.test.ts b/app/api/listings/__tests__/route.test.ts
index a2828b9..e1eeda4 100644
--- a/app/api/listings/__tests__/route.test.ts
+++ b/app/api/listings/__tests__/route.test.ts
@@ -22,11 +22,13 @@ jest.mock("@/lib/googleCloud", () => ({
 jest.mock("@/lib/rbac", () => ({
   getSession: jest.fn().mockResolvedValue({
     allowed: true,
-    user: null,
+    user: { email: "seller@ucsd.edu" },
     reason: undefined,
   }),
 }));
 
+const routeParams = (id: string) => ({ params: Promise.resolve({ id }) });
+
 /** import after mocking */
 import { GET, POST } from "@/app/api/listings/route";
 import { GET as GET_BY_ID, PUT, DELETE } from "@/app/api/listings/[id]/route";
@@ -127,7 +129,7 @@ describe("API: Successful Responses", () => {
       (getListing as jest.Mock).mockResolvedValue(listingData);
 
       const req = new Request(`http://localhost/api/listings/${id}`);
-      const res = await GET_BY_ID(req, { params: { id: id } });
+      const res = await GET_BY_ID(req, routeParams(id));
       const body = await res.json();
 
       expect(res.status).toEqual(200);
@@ -212,6 +214,7 @@ describe("API: Successful Responses", () => {
           price: 50,
           expiryDate: new Date(listingData.expiryDate),
           hazardTags: ["Physical", "Chemical"],
+          sellerEmail: "seller@ucsd.edu",
         })
       );
     });
@@ -264,6 +267,7 @@ describe("API: Successful Responses", () => {
       expect(addListing).toHaveBeenCalledWith(
         expect.objectContaining({
           imageUrls: [],
+          sellerEmail: "seller@ucsd.edu",
         })
       );
     });
@@ -371,7 +375,7 @@ describe("API: Successful Responses", () => {
         body: formData,
       });
 
-      const res = await PUT(req, { params: { id } });
+      const res = await PUT(req, routeParams(id));
       const body = await res.json();
 
       expect(res.status).toBe(200);
@@ -403,7 +407,7 @@ describe("API: Successful Responses", () => {
       const req = new Request(`http://localhost/api/listings/${id}`, {
         method: "DELETE",
       });
-      const res = await DELETE(req, { params: { id } });
+      const res = await DELETE(req, routeParams(id));
       const body = await res.json();
 
       expect(res.status).toBe(200);
@@ -464,7 +468,7 @@ describe("API: Error Responses", () => {
       (connectToDatabase as jest.Mock).mockRejectedValue(new Error("DB Error"));
 
       const req = new Request(`http://localhost/api/listings/${id}`);
-      const res = await GET_BY_ID(req, { params: { id: id } });
+      const res = await GET_BY_ID(req, routeParams(id));
       const body = await res.json();
 
       expect(res.status).toBe(500);
@@ -478,7 +482,7 @@ describe("API: Error Responses", () => {
       (connectToDatabase as jest.Mock).mockResolvedValue({});
 
       const req = new Request(`http://localhost/api/listings/${id}`);
-      const res = await GET_BY_ID(req, { params: { id: id } });
+      const res = await GET_BY_ID(req, routeParams(id));
       const body = await res.json();
 
       expect(res.status).toBe(400);
@@ -495,7 +499,7 @@ describe("API: Error Responses", () => {
       (getListing as jest.Mock).mockResolvedValue(null);
 
       const req = new Request(`http://localhost/api/listings/${id}`);
-      const res = await GET_BY_ID(req, { params: { id: id } });
+      const res = await GET_BY_ID(req, routeParams(id));
       const body = await res.json();
 
       expect(res.status).toBe(404);
@@ -511,7 +515,7 @@ describe("API: Error Responses", () => {
       (getListing as jest.Mock).mockRejectedValue(new Error("DB Error"));
 
       const req = new Request(`http://localhost/api/listings/${id}`);
-      const res = await GET_BY_ID(req, { params: { id: id } });
+      const res = await GET_BY_ID(req, routeParams(id));
       const body = await res.json();
 
       expect(res.status).toBe(500);
@@ -621,7 +625,7 @@ describe("API: Error Responses", () => {
         method: "PUT",
         body: formData,
       });
-      const res = await PUT(req, { params: { id } });
+      const res = await PUT(req, routeParams(id));
       const body = await res.json();
 
       expect(res.status).toBe(500);
@@ -643,7 +647,7 @@ describe("API: Error Responses", () => {
         method: "PUT",
         body: formData,
       });
-      const res = await PUT(req, { params: { id } });
+      const res = await PUT(req, routeParams(id));
       const body = await res.json();
 
       expect(res.status).toBe(400);
@@ -665,7 +669,7 @@ describe("API: Error Responses", () => {
         body: formData,
       });
 
-      const res = await PUT(req, { params: { id } });
+      const res = await PUT(req, routeParams(id));
       const body = await res.json();
 
       expect(res.status).toBe(400);
@@ -688,7 +692,7 @@ describe("API: Error Responses", () => {
         method: "PUT",
         body: formData,
       });
-      const res = await PUT(req, { params: { id } });
+      const res = await PUT(req, routeParams(id));
       const body = await res.json();
 
       expect(res.status).toBe(404);
@@ -717,7 +721,7 @@ describe("API: Error Responses", () => {
         method: "PUT",
         body: formData,
       });
-      const res = await PUT(req, { params: { id } });
+      const res = await PUT(req, routeParams(id));
       const body = await res.json();
 
       expect(res.status).toBe(500);
@@ -741,7 +745,7 @@ describe("API: Error Responses", () => {
       const req = new Request(`http://localhost/api/listings/${id}`, {
         method: "DELETE",
       });
-      const res = await DELETE(req, { params: { id } });
+      const res = await DELETE(req, routeParams(id));
       const body = await res.json();
 
       expect(res.status).toBe(500);
@@ -757,7 +761,7 @@ describe("API: Error Responses", () => {
       const req = new Request(`http://localhost/api/listings/${id}`, {
         method: "DELETE",
       });
-      const res = await DELETE(req, { params: { id } });
+      const res = await DELETE(req, routeParams(id));
       const body = await res.json();
 
       expect(res.status).toBe(400);
@@ -776,7 +780,7 @@ describe("API: Error Responses", () => {
       const req = new Request(`http://localhost/api/listings/${id}`, {
         method: "DELETE",
       });
-      const res = await DELETE(req, { params: { id } });
+      const res = await DELETE(req, routeParams(id));
       const body = await res.json();
 
       expect(res.status).toBe(404);
@@ -794,7 +798,7 @@ describe("API: Error Responses", () => {
       const req = new Request(`http://localhost/api/listings/${id}`, {
         method: "DELETE",
       });
-      const res = await DELETE(req, { params: { id } });
+      const res = await DELETE(req, routeParams(id));
       const body = await res.json();
 
       expect(res.status).toBe(500);
diff --git a/app/api/listings/route.ts b/app/api/listings/route.ts
index f03c352..48bb8d9 100644
--- a/app/api/listings/route.ts
+++ b/app/api/listings/route.ts
@@ -114,10 +114,10 @@ async function GET(request: Request) {
  * @returns JSON response with success message and req body echoed
  */
 async function POST(request: Request) {
-    const { allowed, reason } = await getSession("listing:create");
-    if (!allowed) {
+    const { allowed, reason, user } = await getSession("listing:create");
+    if (!allowed || !user?.email) {
         return NextResponse.json(
-            { success: false, message: reason },
+            { success: false, message: reason ?? "Unauthenticated" },
             { status: 403 }
         );
     }
@@ -181,6 +181,7 @@ async function POST(request: Request) {
         const listingData = {
             ...parsedBody.data,
             imageUrls,
+            sellerEmail: user.email,
             createdAt: new Date(),
         } as ListingInput;
         const listing = await addListing(listingData);
diff --git a/app/listings/[id]/page.tsx b/app/listings/[id]/page.tsx
index d9cdeee..13df374 100644
--- a/app/listings/[id]/page.tsx
+++ b/app/listings/[id]/page.tsx
@@ -10,16 +10,20 @@ interface ListingPageProps {
   }>;
 }
 
-/**
- * Resolve a contact email for the listing until proper transaction
- * functionality exists.
- */
-function getListingContactEmail() {
-  return (
+function isUsableEmail(email: string) {
+  return email.includes("@") && email.includes(".");
+}
+
+function getContactEmailForListing(listing: Listing) {
+  const seller = listing.sellerEmail?.trim() ?? "";
+  if (seller && isUsableEmail(seller)) {
+    return seller;
+  }
+  const fallback =
     process.env.NEXT_PUBLIC_MARKETPLACE_CONTACT_EMAIL ??
     process.env.MARKETPLACE_CONTACT_EMAIL ??
-    "marketplace@lab.example"
-  );
+    "";
+  return fallback.trim();
 }
 
 /**
@@ -57,7 +61,7 @@ export default async function ListingPage({ params }: ListingPageProps) {
 
     return (
       <ListingDetails
-        contactEmail={getListingContactEmail()}
+        contactEmail={getContactEmailForListing(listing)}
         listing={listing}
       />
     );
@@ -66,7 +70,7 @@ export default async function ListingPage({ params }: ListingPageProps) {
 
     return (
       <ListingDetails
-        contactEmail={getListingContactEmail()}
+        contactEmail={getContactEmailForListing(fallbackListing)}
         listing={fallbackListing}
       />
     );
diff --git a/components/listings/ContactModal.tsx b/components/listings/ContactModal.tsx
index 73186a8..b684b8f 100644
--- a/components/listings/ContactModal.tsx
+++ b/components/listings/ContactModal.tsx
@@ -90,6 +90,9 @@ export function ContactModal({
     return null;
   }
 
+  const hasValidEmail =
+    contactEmail.includes("@") && contactEmail.includes(".");
+
   return (
     <div className={styles.overlay} onClick={onClose} role="presentation">
       <div
@@ -119,9 +122,13 @@ export function ContactModal({
           directly by email.
         </p>
 
-        <a className={styles.emailLink} href={`mailto:${contactEmail}`}>
-          {contactEmail}
-        </a>
+        {hasValidEmail ? (
+          <a className={styles.emailLink} href={`mailto:${contactEmail}`}>
+            {contactEmail}
+          </a>
+        ) : (
+          <p className={styles.description}>Seller email is not available.</p>
+        )}
 
         <div className={styles.footer}>
           <button
@@ -131,9 +138,19 @@ export function ContactModal({
           >
             Close
           </button>
-          <a className={styles.primaryButton} href={`mailto:${contactEmail}`}>
-            Email Seller
-          </a>
+          {hasValidEmail ? (
+            <a className={styles.primaryButton} href={`mailto:${contactEmail}`}>
+              Email Seller
+            </a>
+          ) : (
+            <button
+              className={styles.primaryButton}
+              disabled
+              type="button"
+            >
+              Email Seller
+            </button>
+          )}
         </div>
       </div>
     </div>
diff --git a/models/Listing.ts b/models/Listing.ts
index 21455a3..53e2e1d 100644
--- a/models/Listing.ts
+++ b/models/Listing.ts
@@ -38,6 +38,7 @@ const listingSchema = new Schema(
                 enum: ["Physical", "Chemical", "Biological", "Other"],
             },
         ],
+        sellerEmail: { type: String, trim: true, lowercase: true },
     },
     {
         toJSON: {