To combat Chinese gold farmers, Blizzard started selling gold in a bit of a roundabout way. For $20, you can buy a WoW token to sell on the auction house. This token can be purchased by a player and traded for 1 month of game time. Some players dont pay a dime to play - gold is not hard to acquire.
Eve Online has been doing that since 2008.
Oh, don’t you worry your sweet little head, we will.