Lol whaaat? This sounds way too good to be true, I wonder what the catch will be. If its legit sign me up! 
Well there are a lot of freelancers out there who are being paid just playing games. I know someone about a year ago and he says that he is earning $500 a month testing and playing games.
So I wouldn't be surprised if GMO is doing the same marketing or strategy or a way to test their games and see how it can be improved by paying someone to go around and play it and found exploits or gives feedback about the game itself. Its been a gaming practice for many years.