Of course you're not. And the developers should stop whinning. I bought a new copy of Final Fantasy XIII, because I wanted to support them for putting so much effort in one game, but I got a used one for Golden Axe and Lair, since they both flopped and by buying them I wouldn't help them at all. Support anyone you want and don't feel bad about it.
Even indie games like Torchlight get decent sales, when the customers appreciate the effort. My advice: buy only old used games and only when you save much money. Getting a used game for $55 is a total rip-off.
Besides you are helping the industry in general, since many gamers sell their old games to buy new ones. I know a lot of people who sold 1 or 2 used games to get Yakuza 3 or MW:2. And the argument that this is worse than piracy is not necessarily valid. I bought a used copy of Folklore a few ago just because I thought that since it's very cheap I might as well give it a try, but the game was never on my wish list.
