Before I say anything, I can't decide or remember if this action (selling/buying a game card for in-game gold) is considered a violation of the ToS by Blizzard, so if it is, please delete/lock/whatever with the thread, along with my apologies.
Now, in a case someone is buying or selling a game card: how do both sides ensure that everything is ok? Game Card code being given and gold being given as well. How much gold does someone pay/you've paid for a game card?
Thanks in advance.