I'm thinking about buying a used DS game from the online Best Buy website...

I'm thinking about buying a used DS game from the online Best Buy website, and i was wondering what the chances are the game has something wrong with it? for example, dirt on those golden "lines" on the DS cart? I don't want to buy the game and then find out something is wrong with it later on. My thinking is somebody may have had a good reason for selling it, in that something was wrong with it, and the seller wanted to make some money by selling a game that might have problems with it.