I live in the Netherlands where we don't have a gamestop. We have some other smaller stores where you can sell your second hand games to, but not many people do that. If I sell my games, or if I want to buy a second hand game, I go to a website called marktplaats (=marketplace). It's a bit the same as ebay, but you don't have to pay the website anything and your advertisement will be available on the website for 28 days for free. In this way you can cut the "middle man" and  sell directly to other people without some big company who wants a piece of the pie. I don't understand why people sell their games to places like gamestop when they're "screwing" their custumers over by asking a ridiculous prices. Why do people sell their used games to stores that give them less money than if some consumer would buy the game directly from them and why do people buy these ridiculously overpriced second hand games?

because its easy and simple. duh.

Speed and convenience.

People would rather pay a premium to not have to wait for auctions to finish, wait for delivery, wait for payment. What could take weeks or longer can be done securely in 5 minutes at the store.

most people don't like to do stuff themselves

what you are talking about is efficient but wastes time.

?? haven't you seen the rise of gamemania and the thousand of secondhand copies they are selling in the netherlands?

its way quicker.

As others have said, it's faster.
But they do screw you over big time though. When the Wii launched I sold my GameCube (which was perfectly fine) and they only gave me $10 for it :/

A mixture of laziness and stupidity

Others have highlighted the simplicity, but it should go without saying that there is also greater security involved with secondhand sellers. You can be secure in the knowledge that they will buy, and secure in the knowledge that you're buying quality merchandise. The reality of peer to peer transactions is that there are real risks. You can easily end up being overcharged, undervalued, or outright burned. In the end it is entirely a higher risk higher reward scenario.

There is a lot that can go wrong, and you are entirely alone if it does go wrong. You are placing faith in the decency of another person who may not have scruples. You could end up buying resurrected merchandise such as a console with its mother board soldered down, or a game disk that has been buffed paper thin. You could end up overpaying for something. It isn't uncommon to see peer to peer copies of games being sold for more then what the secondhand stores are charging. While games that are short priced will sit unsold forever.

I am not arguing against peer to peer trading. Hell I have bought, traded, and sold peer to peer over a hundred times in my life. That isn't to say I haven't done well with that, but it also doesn't mean that I haven't been burned. I think I came out better for the hands on wheeling and dealing, but thanks to secondhand stores there are some things I am never going to take a gamble on again. So in the end I am not just against second hand stores. There are things I will only buy there, and there are things I will not sell or buy there.

Craigslist helps me with my game sales. I have had money in my hand 30 minutes after posting before. That's real money not just store credit.