Many people refuse to buy used games because of a percieved lower quality, but the reality is that a DVD is a LOT harder to damage than people think, a few shallow scratches are not going to effect the game at all, especially with multi-layed DVDs. Used games are generally a fraction of the price of brand-new retail games.
Before buying a used game, a shopkeeper must first test it to make sure it's playable, if you have ever sold a game or system you will know how strict the tests are. It is almost impossible for a damaged game to slip through the net.
I have bought over 60 games second hand, and i have never had a single problem with any of them. I also bought a used Xbox 360, notorious for overheating and having problems, and it has never let me down after 3 years.
Every reputable game shop sells, trades and buys used games, and many thrift stores and pawn shops have a wide selection, never avoid a shop because it looks cheap. The prices of games are on the rise, and it is well worth waiting a couple of months after a game hes been released and buying a used version at half of the retail price.