By getting a small subset of players to buy premium cosmetic content and in-game gold. Blizzard came up with a clever mechanism involving game time and other players for the latter, both in order to obfuscate what they were doing somewhat and to give them a little more control over their economy.

The Blizzard Warcraft Store: https://us.battle.net/shop/en/product/game/wow

Information on the "WoW Token" mechanism for turning $ into gold: http://www.tentonhammer.com/guides/guide-to-buying-and-selli...