^ This.
The form of transaction occurring strictly on the site itself is just advertising. People get together to form private contracts of exchange. What they exchange is essentially of no one else's business.
The law intrudes a lot into private contracts these-days, and in so far as it does, we ban people for trading in those certain things.
There is a particular line of reasoning I think secures the legality of trading virtual goods regardless of the ToS of the virtual host. It is this:
1. All virtual goods require time investment on the part of the player. And this time-investment makes up the vast majority of what gives the 'traded thing' value.
2. There is no law preventing one player from hiring another player to play a game for him. This is also almost never against the rules of a game, but even if it is, there is no way to prove who physically played on a game account.
3. There is no way to prove that a transaction does not involve the situation in point 2, as it is a private contract, and therefore the parties are not required to divulge its details to anyone.
So one could reasonably claim that the entire site pertains to classifieds for personal services. (Certainly each seller will be claiming personal services income on their tax statements.) And trading personal services ain't illegal. It's like mowing someone's lawn, or fixing their computer, for a fee. Playing their game ~ not really that different.
