In-Game Marketplace & Player Trading System

ROLE: You are a virtual economy architect who has designed player trading systems for MMOs and multiplayer games. You understand real-money trading (RMT) threats, market manipulation tactics, price discovery mechanisms, and how player-driven economies can either thrive as rich gameplay systems or collapse into inflation spirals. You draw from both game design and real-world economic principles.

OBJECTIVE: Design a player trading system that enables meaningful economic gameplay, prevents exploitation and fraud, maintains healthy price levels, and creates emergent market dynamics that keep players engaged.

TASK:
Design a marketplace and trading system for the following game:

**Game Type:** {{GAME_TYPE}} (e.g., MMO RPG, survival crafting, trading card game, sandbox)
**Economy Type:** {{ECONOMY_TYPE}} (e.g., fully player-driven like EVE, guided like WoW AH, restricted like Diablo 3)
**Tradeable Items:** {{TRADEABLE_ITEMS}} (e.g., all items, equipment only, materials only, cosmetics only)
**Player Base Size:** {{PLAYER_BASE}} expected concurrent traders
**RMT Stance:** {{RMT_STANCE}} (e.g., strictly prohibited, tolerated, officially supported via exchange)

Provide the following system design:

1. **Marketplace Architecture:**
   - Listing system: auction (timed bidding), buy-order/sell-order (stock exchange style), fixed price, or hybrid
   - Search and filter capabilities: by item type, rarity, stats, price range, seller reputation
   - Price display: current price, historical price chart, volume indicators, price trend arrows
   - Regional vs. global marketplace: server-specific or cross-server trading
   - Mobile/companion app access: out-of-game trading capabilities

2. **Transaction Mechanics:**
   - Listing fees: flat fee vs. percentage, paid upfront vs. deducted from sale
   - Transaction tax: percentage taken as a currency sink, scaling with item value
   - Listing duration: 12h, 24h, 48h options with different fee structures
   - Buyout vs. bidding: pros/cons for each item category
   - Bulk trading: batch listing tools, commodity stacking
   - Trade escrow: how items and currency are held during transaction
   - Cancellation policies: fee for delisting, cooldown before relisting

3. **Anti-Manipulation Measures:**
   - Price floor/ceiling mechanisms: how to prevent items being listed at absurd prices (1 gold or 999999 gold) for RMT transfers
   - Velocity detection: flagging accounts that trade unusual volumes or values
   - New account restrictions: trading cooldowns for fresh accounts, progressive trading limits tied to account age and activity
   - Sniper protection: anti-last-second bid mechanics, bid extension timers
   - Collusion detection: identifying ring-trading patterns, wash trading, price fixing groups
   - Automated vs. manual review: which transactions get auto-flagged, what triggers human review

4. **Price Stabilization Systems:**
   - NPC vendor buy/sell prices as soft price anchors
   - Commodity sinks that remove items from circulation (crafting consumption, item degradation, binding-on-use)
   - Supply control: drop rate adjustments based on market saturation metrics
   - Demand drivers: new content that creates demand for previously low-value items
   - Emergency levers: what the dev team can do if a market crash or hyperinflation occurs

5. **Player Experience Design:**
   - First-time seller onboarding: tutorial for listing items, understanding market data
   - Price suggestion algorithm: analyzing recent sales to recommend listing prices
   - Notification system: sold item alerts, watchlist price alerts, bid outbid warnings
   - Transaction history: detailed log with profit/loss tracking
   - Reputation system: seller ratings, trade completion rate, dispute history
   - Favorite sellers/buyers: relationship building between traders

6. **Economy Health Dashboard (Dev Tools):**
   - Key metrics: total transaction volume, average item prices by category, currency velocity, wealth distribution Gini coefficient
   - Alert systems: unusual price movements, suspected bot trading patterns, currency sink vs. source imbalance
   - Simulation tools: model impact of drop rate changes or new item introductions before going live
   - Historical analysis: seasonal patterns, patch impact correlation, player behavior shifts