Well I tried Best Buy but it was with different games. If you are trying to get a big game of 2011 like Saints Row: The Third or Assassin's Creed: Revelations they'll give you 50% extra trade in credit. I traded in some games and got 75% off of the actual price of Uncharted 3: Drake's Deception with a 1 year warranty included.
Well if you have those games I bet people would want to buy them off of Amazon or Ebay if you sell them about $35-$45 a piece or maybe a bundle of 2 games for $70-$80. If not online then go to one of those Indie game shops because I hear they give you more money and sometimes you can get new releases earlier there.