As much as I wouldn't want to do this, and I generally like the Consumerist's articles, it's often a part of law enforcement, as Gamestop is generally required to abide by "pawn shop law." It's going to be the same at Best Buy's and Mom n Pop shops in the same areas that take in the same volume of trades for cash.
PROTIP: You get more out of your used games selling them on Ebay anyway. Stop screwing yourself by going to gamestop