The sheriff of Broward County, Fla. (Fort Lauderdale) says Florida law requires him to treat used games the same as merchandise sold at pawn shops. That means sellers can't go home with their cash (or store credit) without leaving a greasy smudge.
According to the New Times of Broward-Palm Beach, the sheriff sent deputies to every game store in the county in October, telling them to get thumbprints from all used-game sellers. A GameStop manager breaks it down pretty succinctly when asked why he complied: "They have guns. I don't argue with people with guns." That's exactly what law enforcement wants to hear, son.
A sheriff's spokeswoman said the requirement is part of a state law passed in 2007. That law also requires sellers to put a 15-day hold on the items before they can resell them, but as you can guess, probably no one is complying with that. The GameStop manager said that most customers don't care about the requirement, although some have left the store without selling games.
Of course it's meant to cut down on people selling stolen merch, and games and game systems are top items in that category. It's also another way to make law abiding private citizens feel like they're criminals.
Sell Your Used Games, Get Thumbprinted [Sports Legends, thanks Madgame]