When you're going to trade or sell a game in, you obviously are in the business to make a buck. The company or person your trading or selling to is obviously trying to save a buck. Now lets all be honest, GameStop does rip people off, and they accept it for the convenience. They'll also kick you out of the store if you try to buy a game from somebody who is there to sell or trade in a game by offering them more. [spoiler]First hand experience.[/spoiler]
Well now I can honestly tell you that BestBuy could easily top that. This is there disclaimer for the trade in section of there website.
"We will not accept more than 3 games of the same title and platform from a customer (or address) in a year. Please do not submit more than the limit as excess submissions WILL NOT BE RETURNED."
-TwisT