I wouldn't recommend that, this may lead to report which consequence is ban. This is like trading game currency for real cash. Of course there's a lot of people who buy Game cards via game gold but is highly dangerous. Also there a huge scam risk. For me it is a bad idea. Better try to sell your gold via vanilla account and then try to buy a game card for real money. Selling gold is also bannable but there is a less risk than previous situation, because you sell to sites and you don't spam trade chat with offers.
