I wonder what the exchange rate is for fake gold.
It depends on how popular the game is. Because people need game gold to pretty much do anything in games, they are often willing to pay real money to get the gold, since it is easier to get real money than game gold. For example, in China, "gold farmers" basically work in a sweat-shop-like environment playing games like World of Warcraft, earning game gold that their employers then sell for real money (dollars or Euros). Sometimes, the gold farmers are prisoners who are forced to play the games for hours on end. The gold sellers often aggressively market the gold, contacting players in game, sending them emails, or broadcasting advertisements through the game chat channels.
There is a whole sordid industry built around selling game gold for real money to people who don't want to earn it honestly through game "jobs."