Michael Arrington from TechCrunch takes a closer look at the social gaming ecosystem of Facebook games like FarmVille. The site argues these kind of games earn money in an unethical way, because they scam users into participating in lead offers to earn in-game currency. Here's an example of one of these scams, in this particular case the user is fooled into getting a $9.99 a month subscription to get 47 farm cash for FarmVille:
A typical scam: users are offered in game currency in exchange for filling out an IQ survey. Four simple questions are asked. The answers are irrelevant. When the user gets to the last question they are told their results will be text messaged to them. They are asked to enter in their mobile phone number, and are texted a pin code to enter on the quiz. Once they’ve done that, they’ve just subscribed to a $9.99/month subscription. Tatto Media is the company at the very end of the line on most mobile scams, and they flow it up through Offerpal, SuperRewards and others to the game developers.
As you can see in the image below, nothing in the offer says that the user will be billed $10/month forever for a useless service.