I think the previous commenter meant real-life economies, not in-game ones so much. Although with any MMO or any multiplayer game with trading for that matter,

I think the previous commenter meant real-life economies, not in-game ones so much. Although with any MMO or any multiplayer game with trading for that matter, there will be a grey market of trading items, gold, or characters for real money, and a bot market to go with it.