diff --git a/packages/api-server/src/routes/ebay.ts b/packages/api-server/src/routes/ebay.ts
index 21f0730..48652b7 100644
--- a/packages/api-server/src/routes/ebay.ts
+++ b/packages/api-server/src/routes/ebay.ts
@@ -21,8 +21,20 @@ export async function ebayRoute(req: Request): Promise<Response> {
 
     const minPriceParam = reqUrl.searchParams.get("minPrice");
     const minPrice = minPriceParam ? parseInt(minPriceParam, 10) : undefined;
+    if (minPriceParam && Number.isNaN(minPrice)) {
+      return Response.json(
+        { message: "Invalid minPrice parameter" },
+        { status: 400 },
+      );
+    }
     const maxPriceParam = reqUrl.searchParams.get("maxPrice");
     const maxPrice = maxPriceParam ? parseInt(maxPriceParam, 10) : undefined;
+    if (maxPriceParam && Number.isNaN(maxPrice)) {
+      return Response.json(
+        { message: "Invalid maxPrice parameter" },
+        { status: 400 },
+      );
+    }
     const strictMode = reqUrl.searchParams.get("strictMode") === "true";
     const buyItNowOnly = reqUrl.searchParams.get("buyItNowOnly") !== "false";
     const canadaOnly = reqUrl.searchParams.get("canadaOnly") !== "false";
@@ -71,28 +83,11 @@ export async function ebayRoute(req: Request): Promise<Response> {
         { status: 404 },
       );
 
-    let results;
-    if (hideUnstableResults) {
-      const limitedResults =
-        maxItems !== undefined
-          ? items.results.slice(0, maxItems)
-          : items.results;
-      const remainingSlots =
-        maxItems !== undefined
-          ? Math.max(0, maxItems - limitedResults.length)
-          : undefined;
-      const limitedUnstable =
-        remainingSlots !== undefined
-          ? items.unstableResults.slice(0, remainingSlots)
-          : items.unstableResults;
-      results = {
-        results: limitedResults,
-        unstableResults: limitedUnstable,
-      };
-    } else {
-      results =
-        maxItems !== undefined ? items.slice(0, maxItems) : items;
-    }
+    const results = hideUnstableResults
+      ? items
+      : maxItems !== undefined
+        ? items.slice(0, maxItems)
+        : items;
 
     return Response.json(results, { status: 200 });
   } catch (error) {
diff --git a/packages/api-server/src/routes/kijiji.ts b/packages/api-server/src/routes/kijiji.ts
index 153824c..f6aa972 100644
--- a/packages/api-server/src/routes/kijiji.ts
+++ b/packages/api-server/src/routes/kijiji.ts
@@ -19,10 +19,28 @@ export async function kijijiRoute(req: Request): Promise<Response> {
 
   const maxPagesParam = reqUrl.searchParams.get("maxPages");
   const maxPages = maxPagesParam ? parseInt(maxPagesParam, 10) : 5;
+  if (maxPagesParam && Number.isNaN(maxPages)) {
+    return Response.json(
+      { message: "Invalid maxPages parameter" },
+      { status: 400 },
+    );
+  }
   const priceMinParam = reqUrl.searchParams.get("priceMin");
   const priceMin = priceMinParam ? parseInt(priceMinParam, 10) : undefined;
+  if (priceMinParam && Number.isNaN(priceMin)) {
+    return Response.json(
+      { message: "Invalid priceMin parameter" },
+      { status: 400 },
+    );
+  }
   const priceMaxParam = reqUrl.searchParams.get("priceMax");
   const priceMax = priceMaxParam ? parseInt(priceMaxParam, 10) : undefined;
+  if (priceMaxParam && Number.isNaN(priceMax)) {
+    return Response.json(
+      { message: "Invalid priceMax parameter" },
+      { status: 400 },
+    );
+  }
   const hideUnstableResults =
     reqUrl.searchParams.get("unstableFilter") === "true";
 
diff --git a/packages/api-server/test/routes.test.ts b/packages/api-server/test/routes.test.ts
index 2c221f6..3ec8d6c 100644
--- a/packages/api-server/test/routes.test.ts
+++ b/packages/api-server/test/routes.test.ts
@@ -399,7 +399,7 @@ describe("API routes", () => {
     expect(body).toHaveLength(0);
   });
 
-  test("ebayRoute limits total items with maxItems in unstable mode", async () => {
+  test("ebayRoute passes through scraper payload unchanged in unstable mode", async () => {
     const { ebayRoute } = await import("../src/routes/ebay");
 
     fetchEbayItems.mockImplementation(() =>
@@ -416,10 +416,8 @@ describe("API routes", () => {
     );
 
     const body = await response.json();
-    const total = body.results.length + body.unstableResults.length;
-    expect(total).toBe(4);
     expect(body.results).toHaveLength(3);
-    expect(body.unstableResults).toHaveLength(1);
+    expect(body.unstableResults).toHaveLength(2);
     expect(body.results[0].title).toBe("a");
     expect(body.unstableResults[0].title).toBe("d");
   });
@@ -472,4 +470,74 @@ describe("API routes", () => {
     const body = await response.json();
     expect(body.message).toBe("Invalid maxItems parameter");
   });
+
+  test("ebayRoute returns 400 for invalid minPrice", async () => {
+    const { ebayRoute } = await import("../src/routes/ebay");
+
+    const response = await ebayRoute(
+      new Request(
+        "http://localhost/api/ebay?q=laptop&minPrice=abc",
+      ),
+    );
+
+    expect(response.status).toBe(400);
+    const body = await response.json();
+    expect(body.message).toBe("Invalid minPrice parameter");
+  });
+
+  test("ebayRoute returns 400 for invalid maxPrice", async () => {
+    const { ebayRoute } = await import("../src/routes/ebay");
+
+    const response = await ebayRoute(
+      new Request(
+        "http://localhost/api/ebay?q=laptop&maxPrice=abc",
+      ),
+    );
+
+    expect(response.status).toBe(400);
+    const body = await response.json();
+    expect(body.message).toBe("Invalid maxPrice parameter");
+  });
+
+  test("kijijiRoute returns 400 for invalid maxPages", async () => {
+    const { kijijiRoute } = await import("../src/routes/kijiji");
+
+    const response = await kijijiRoute(
+      new Request(
+        "http://localhost/api/kijiji?q=laptop&maxPages=abc",
+      ),
+    );
+
+    expect(response.status).toBe(400);
+    const body = await response.json();
+    expect(body.message).toBe("Invalid maxPages parameter");
+  });
+
+  test("kijijiRoute returns 400 for invalid priceMin", async () => {
+    const { kijijiRoute } = await import("../src/routes/kijiji");
+
+    const response = await kijijiRoute(
+      new Request(
+        "http://localhost/api/kijiji?q=laptop&priceMin=abc",
+      ),
+    );
+
+    expect(response.status).toBe(400);
+    const body = await response.json();
+    expect(body.message).toBe("Invalid priceMin parameter");
+  });
+
+  test("kijijiRoute returns 400 for invalid priceMax", async () => {
+    const { kijijiRoute } = await import("../src/routes/kijiji");
+
+    const response = await kijijiRoute(
+      new Request(
+        "http://localhost/api/kijiji?q=laptop&priceMax=abc",
+      ),
+    );
+
+    expect(response.status).toBe(400);
+    const body = await response.json();
+    expect(body.message).toBe("Invalid priceMax parameter");
+  });
 });