diff --git a/.changeset/fix-discovered-sales-agents-misclassified-as-buying.md b/.changeset/fix-discovered-sales-agents-misclassified-as-buying.md
new file mode 100644
index 0000000000..2b7fece1ce
--- /dev/null
+++ b/.changeset/fix-discovered-sales-agents-misclassified-as-buying.md
@@ -0,0 +1,8 @@
+---
+---
+
+Fix discovered sales agents being registered as `type: "buying"` instead of `type: "sales"`.
+
+The capability-discovery code was inferring `'buying'` from `SALES_TOOLS` (`get_products`, `create_media_buy`, `list_authorized_properties`) — semantically backwards: these tools are exposed by **sell-side** agents authorized to sell on behalf of publishers. Three inference sites are corrected (`server/src/capabilities.ts` × 2, `server/src/db/agent-context-db.ts`), and migration `454_fix_misclassified_sales_agents.sql` flips existing `'buying'` → `'sales'` rows in both `discovered_agents.agent_type` (the crawler only re-infers `'unknown'` rows, so the misclassification was sticky) AND `agent_capabilities_snapshot.inferred_type` (read by `registry-api.ts` and by PR #3498's prevention layer — stale rows there would silently override a correctly-supplied `'sales'` back to `'buying'`).
+
+Closes #3495.
diff --git a/server/src/capabilities.ts b/server/src/capabilities.ts
index 77b29119c5..1a031eb58c 100644
--- a/server/src/capabilities.ts
+++ b/server/src/capabilities.ts
@@ -213,16 +213,23 @@ export class CapabilityDiscovery {
   }
 
   /**
-   * Infer agent type from discovered tools.
-   * Buying agents have: get_products, create_media_buy, list_authorized_properties
-   * Creative agents have: list_creative_formats, build_creative, validate_creative
-   * Signals agents have: get_signals, match_audience, activate_signal
+   * Infer agent type from the tool list a remote agent advertises.
+   *
+   * The discovery vector is "what tools does this agent EXPOSE" — sell-side
+   * agents publish get_products / create_media_buy / list_authorized_
+   * properties for buyers to call; buy-side agents typically do NOT
+   * advertise those (they call them). So advertising SALES_TOOLS maps to
+   * type 'sales'. Buy-side agents are not reliably typed from this signal
+   * and return 'unknown' until a stronger source (e.g. member self-
+   * registration) sets the type.
    */
-  private inferAgentType(tools: ToolCapability[]): 'buying' | 'creative' | 'signals' | 'unknown' {
+  private inferAgentType(tools: ToolCapability[]): 'sales' | 'creative' | 'signals' | 'unknown' {
     const toolNames = new Set(tools.map((t) => t.name.toLowerCase()));
 
-    // Priority: buying > creative > signals (buying is the primary commerce type)
-    if (CapabilityDiscovery.SALES_TOOLS.some(t => toolNames.has(t))) return 'buying';
+    // Priority: sales > creative > signals when an agent advertises tools
+    // from multiple buckets — sell-side wins because the rest of the
+    // registry UI treats it as the primary integration surface.
+    if (CapabilityDiscovery.SALES_TOOLS.some(t => toolNames.has(t))) return 'sales';
     if (CapabilityDiscovery.CREATIVE_TOOLS.some(t => toolNames.has(t))) return 'creative';
     if (CapabilityDiscovery.SIGNALS_TOOLS.some(t => toolNames.has(t))) return 'signals';
 
@@ -297,8 +304,8 @@ export class CapabilityDiscovery {
    * Infer agent type from a capability profile.
    * Use this to avoid duplicating the type inference logic.
    */
-  inferTypeFromProfile(profile: AgentCapabilityProfile): 'buying' | 'creative' | 'signals' | 'unknown' {
-    if (profile.standard_operations) return 'buying';
+  inferTypeFromProfile(profile: AgentCapabilityProfile): 'sales' | 'creative' | 'signals' | 'unknown' {
+    if (profile.standard_operations) return 'sales';
     if (profile.creative_capabilities) return 'creative';
     if (profile.signals_capabilities) return 'signals';
     return 'unknown';
diff --git a/server/src/db/agent-context-db.ts b/server/src/db/agent-context-db.ts
index 2ba2fdbd20..164fcda049 100644
--- a/server/src/db/agent-context-db.ts
+++ b/server/src/db/agent-context-db.ts
@@ -989,7 +989,7 @@ export class AgentContextDatabase {
    */
   inferAgentType(tools: string[]): AgentType {
     if (tools.includes('get_products') || tools.includes('create_media_buy')) {
-      return 'buying';
+      return 'sales';
     }
     if (tools.includes('list_creative_formats') && !tools.includes('get_products')) {
       return 'creative';
diff --git a/server/src/db/migrations/454_fix_misclassified_sales_agents.sql b/server/src/db/migrations/454_fix_misclassified_sales_agents.sql
new file mode 100644
index 0000000000..bf1ec61875
--- /dev/null
+++ b/server/src/db/migrations/454_fix_misclassified_sales_agents.sql
@@ -0,0 +1,33 @@
+-- Fix sales agents misclassified as 'buying' in the federated discovery index.
+--
+-- Migration 387 renamed sales -> buying everywhere. Migration 392 restored
+-- 'sales' as a valid agent_type but did not back-fill discovered_agents, and
+-- the inference code in server/src/capabilities.ts continued to return
+-- 'buying' for SALES_TOOLS (get_products / create_media_buy /
+-- list_authorized_properties). Every row with the value 'buying' in either
+-- table below was inferred from those sales tools and is therefore a sell-
+-- side agent, not a buy-side agent.
+--
+-- Two tables need fixing:
+--
+--   1. discovered_agents.agent_type
+--      The crawler's refreshAgentSnapshots only re-infers when the existing
+--      type is 'unknown', so without this back-fill the misclassification
+--      is sticky even after the inference fix in capabilities.ts.
+--
+--   2. agent_capabilities_snapshot.inferred_type
+--      Read by registry-api.ts:3465-3467 (to fill in agent type when the
+--      registered type is 'unknown') and by the prevention layer in PR
+--      #3498's resolveAgentTypes() (as the authoritative type source for
+--      every member-profile write). Stale 'buying' values here would cause
+--      the prevention layer to OVERRIDE a correctly client-supplied 'sales'
+--      back to 'buying' for any agent probed before the inference fix
+--      shipped. Same root cause, same fix.
+
+UPDATE discovered_agents
+  SET agent_type = 'sales'
+  WHERE agent_type = 'buying';
+
+UPDATE agent_capabilities_snapshot
+  SET inferred_type = 'sales'
+  WHERE inferred_type = 'buying';
diff --git a/tests/capabilities.test.ts b/tests/capabilities.test.ts
index 8c9c081c74..e25a5445a6 100644
--- a/tests/capabilities.test.ts
+++ b/tests/capabilities.test.ts
@@ -11,17 +11,17 @@ describe("CapabilityDiscovery", () => {
         tools.map((t) => ({ name: t.name, description: "", input_schema: {}, verified_at: "" }))
       );
 
-    it("should infer buying type from buying-specific tools", () => {
-      expect(inferAgentType([{ name: "get_products" }])).toBe("buying");
-      expect(inferAgentType([{ name: "create_media_buy" }])).toBe("buying");
-      expect(inferAgentType([{ name: "list_authorized_properties" }])).toBe("buying");
+    it("should infer sales type from sales-specific tools", () => {
+      expect(inferAgentType([{ name: "get_products" }])).toBe("sales");
+      expect(inferAgentType([{ name: "create_media_buy" }])).toBe("sales");
+      expect(inferAgentType([{ name: "list_authorized_properties" }])).toBe("sales");
       expect(
         inferAgentType([
           { name: "get_products" },
           { name: "create_media_buy" },
           { name: "list_authorized_properties" },
         ])
-      ).toBe("buying");
+      ).toBe("sales");
     });
 
     it("should infer creative type from creative-specific tools", () => {
@@ -45,27 +45,27 @@ describe("CapabilityDiscovery", () => {
       expect(inferAgentType([{ name: "ping" }, { name: "health_check" }])).toBe("unknown");
     });
 
-    it("should prioritize buying for multi-type agents", () => {
-      // Both buying and creative tools → buying (primary commerce type)
+    it("should prioritize sales for multi-type agents", () => {
+      // Both sales and creative tools → sales (primary commerce type)
       expect(
         inferAgentType([{ name: "get_products" }, { name: "list_creative_formats" }])
-      ).toBe("buying");
-      // All three types → buying
+      ).toBe("sales");
+      // All three types → sales
       expect(
         inferAgentType([
           { name: "get_products" },
           { name: "build_creative" },
           { name: "get_signals" },
         ])
-      ).toBe("buying");
-      // Creative + signals (no buying) → creative
+      ).toBe("sales");
+      // Creative + signals (no sales) → creative
       expect(
         inferAgentType([{ name: "build_creative" }, { name: "get_signals" }])
       ).toBe("creative");
     });
 
     it("should handle tool names case-insensitively", () => {
-      expect(inferAgentType([{ name: "GET_PRODUCTS" }])).toBe("buying");
+      expect(inferAgentType([{ name: "GET_PRODUCTS" }])).toBe("sales");
       expect(inferAgentType([{ name: "List_Creative_Formats" }])).toBe("creative");
       expect(inferAgentType([{ name: "MATCH_AUDIENCE" }])).toBe("signals");
     });
@@ -79,7 +79,7 @@ describe("CapabilityDiscovery", () => {
       last_discovered: new Date().toISOString(),
     };
 
-    it("should return buying when standard_operations is present", () => {
+    it("should return sales when standard_operations is present", () => {
       const profile: AgentCapabilityProfile = {
         ...baseProfile,
         standard_operations: {
@@ -91,7 +91,7 @@ describe("CapabilityDiscovery", () => {
           can_list_properties: true,
         },
       };
-      expect(discovery.inferTypeFromProfile(profile)).toBe("buying");
+      expect(discovery.inferTypeFromProfile(profile)).toBe("sales");
     });
 
     it("should return creative when creative_capabilities is present", () => {
@@ -124,9 +124,9 @@ describe("CapabilityDiscovery", () => {
       expect(discovery.inferTypeFromProfile(baseProfile)).toBe("unknown");
     });
 
-    it("should prioritize buying over creative over signals when multiple present", () => {
-      // buying + creative -> buying
-      const buyingAndCreative: AgentCapabilityProfile = {
+    it("should prioritize sales over creative over signals when multiple present", () => {
+      // sales + creative -> sales
+      const salesAndCreative: AgentCapabilityProfile = {
         ...baseProfile,
         standard_operations: {
           can_search_inventory: true,
@@ -143,7 +143,7 @@ describe("CapabilityDiscovery", () => {
           can_preview: false,
         },
       };
-      expect(discovery.inferTypeFromProfile(buyingAndCreative)).toBe("buying");
+      expect(discovery.inferTypeFromProfile(salesAndCreative)).toBe("sales");
 
       // creative + signals -> creative
       const creativeAndSignals: AgentCapabilityProfile = {