Any game that has goods that can be exchanged by players is a potential for illegal money transfers even without the ability to get money back out of the game.

Any game that has goods that can be exchanged by players is a potential for illegal money transfers even without the ability to get money back out of the game. For example, there's a shadow market for both CounterStrike weapon skins and Team Fortress 2 items. Here's how it works: I have a big supply of items. They have an assigned value. You give me money and the name of the receiving party. I send some items to a broker across the planet. They receive the goods, take their big, and give the rest in cash to the receiving party. We have now just made a wire transfer inside of TF2.