Okay, this deal is valid, at least at that specific Best Buy store. I was just there yesterday and they have a small selection of PS3, 360, and DS games that are "buy 1, get 1 free". There are small printed signs above each special section of games. I was in too much of a hurry to scribble down a list, sadly, and it sounds like this is a very specific deal to that individual Best Buy.
I got Castlevania: Order of Ecclesia and Disgae DS for a total of $30.
That was the only real "deal" in the pile of DS stuff, and there was exactly one copy of each. There appeared to be more stuff in the 360 and PS3 piles, though.