I bought 3 DS games for Christmas from Best Buy when they were having a buy 2 get 1 free sale. It turns out my nephew already had one of the games.
I tried to exchange the one he had but was told I couldn't because it was the one I got for free. I told them that I wasn't trying to return the game, just exchange it for one of the same price. Nope, I wasn't allowed. I even talked to a manager.
Since I technically paid $0 for the game, it was only worth $0. I explained that the game was listed as $29.99 on the receipt (even though I paid $0) and I was just exchanging it for another game worth $29.99.
It didn't matter. Apparently they are idiots and don't understand what an exchange is!!