Player-to-player trading systems

1. Pay-to-Win vs Free-to-Play (Virtual Economy Gamification Tips)
2. Game Revenue vs Virtual Revenue (Virtual Economy Gamification Tips)
3. Inflation Rate vs Deflation Rate (Virtual Economy Gamification Tips)
4. Item Rarity vs Item Value (Virtual Economy Gamification Tips)
5. Tradable Items vs Non-Tradable Items (Virtual Economy Gamification Tips)