Unfortunately, buying gold from 3rd parties for the games that the victims play, is not something that is very easily gotten rid of. Hackers are always as fast, if not faster, than security countermeasures.
However, here at Aeria, from what I can see, people buying gold is limited to a small percentage, and they always pay the piper for doing so (in one way or another.) For the most part, it's very much so common knowledge (even to the people here that do decide to buy it, for the most part.)
There's a rule of thumb for being a member of the Aeria community that stays out of trouble: "When in doubt, ask. When in more doubt, ask a GM through RT."
Gold sinks are also limited to the games themselves, and it's up to the developers to put them in, should they so choose. However: Using it as a countermeasure to gold buying may only increase the number of incidents, because people may begin to think it's ok. A gold sink should be implemented as a natural countermeasure to the game's natural economic state. Not as a means for gold buyers to continue.