diff --git a/src/modules/class/class.service.ts b/src/modules/class/class.service.ts
index dc5cff4..7ad4b00 100644
--- a/src/modules/class/class.service.ts
+++ b/src/modules/class/class.service.ts
@@ -1,7 +1,8 @@
-
+```typescript
 import { classes, users } from "@/db/schema";
 import { eq, sql } from "drizzle-orm";
 import { DrizzleClient } from "@/lib/DrizzleClient";
+import { UserError } from "@/lib/errors";
 
 export const classService = {
     getAllClasses: async () => {
@@ -14,7 +15,7 @@ export const classService = {
                 where: eq(classes.id, classId),
             });
 
-            if (!cls) throw new Error("Class not found");
+            if (!cls) throw new UserError("Class not found");
 
             const [user] = await txFn.update(users)
                 .set({ classId: classId })
@@ -37,15 +38,15 @@ export const classService = {
                 where: eq(classes.id, classId),
             });
 
-            if (!cls) throw new Error("Class not found");
+            if (!cls) throw new UserError("Class not found");
 
-            if (amount < 0n && (cls.balance ?? 0n) < -amount) {
-                throw new Error("Insufficient class funds");
+            if ((cls.balance ?? 0n) < amount) {
+                throw new UserError("Insufficient class funds");
             }
 
             const [updatedClass] = await txFn.update(classes)
                 .set({
-                    balance: sql`${classes.balance} + ${amount}`,
+                    balance: sql`${ classes.balance } + ${ amount } `,
                 })
                 .where(eq(classes.id, classId))
                 .returning();
diff --git a/src/modules/quest/quest.service.ts b/src/modules/quest/quest.service.ts
index 3e163c5..b61375e 100644
--- a/src/modules/quest/quest.service.ts
+++ b/src/modules/quest/quest.service.ts
@@ -1,6 +1,7 @@
-
+```typescript
 import { quests, userQuests, users } from "@/db/schema";
 import { eq, and, sql } from "drizzle-orm";
+import { UserError } from "@/lib/errors";
 import { DrizzleClient } from "@/lib/DrizzleClient";
 import { economyService } from "@/modules/economy/economy.service";
 import { levelingService } from "@/modules/leveling/leveling.service";
@@ -45,8 +46,8 @@ export const questService = {
                 }
             });
 
-            if (!userQuest) throw new Error("Quest not assigned");
-            if (userQuest.completedAt) throw new Error("Quest already completed");
+            if (!userQuest) throw new UserError("Quest not assigned");
+            if (userQuest.completedAt) throw new UserError("Quest already completed");
 
             // Mark completed
             await txFn.update(userQuests)
@@ -62,7 +63,7 @@ export const questService = {
 
             if (rewards?.balance) {
                 const bal = BigInt(rewards.balance);
-                await economyService.modifyUserBalance(userId, bal, 'QUEST_REWARD', `Reward for quest ${questId}`, null, txFn);
+                await economyService.modifyUserBalance(userId, bal, 'QUEST_REWARD', `Reward for quest ${ questId }`, null, txFn);
                 results.balance = bal;
             }
 
diff --git a/src/modules/trade/trade.service.ts b/src/modules/trade/trade.service.ts
index 33b4f89..78e4d1b 100644
--- a/src/modules/trade/trade.service.ts
+++ b/src/modules/trade/trade.service.ts
@@ -1,5 +1,7 @@
 import type { TradeSession, TradeParticipant } from "./trade.types";
 import { DrizzleClient } from "@/lib/DrizzleClient";
+import { withTransaction } from "@/lib/db";
+import { UserError } from "@/lib/errors";
 import { economyService } from "@/modules/economy/economy.service";
 import { inventoryService } from "@/modules/inventory/inventory.service";
 import { itemTransactions } from "@/db/schema";