I have a Goozex membership.
It's not a scam or anything, the site makes its money off of the trade credits people buy. It costs $1.00 for 1 trade credit. You don't actually get trade credits for trading in games, you only get Goozex points.
You would need 1 trade credit for every game you want to "buy" off the site, plus the needed amount of Goozex points.
The only way you can get trade credits is either by continuously referring people, or by purchasing the points.
It certainly is a money saver though, the trade in value for most of the games is much more than what you can get from Gamestop or anything so I prefer to trade my games on there. I've traded more than 75 games since I started in 2007 and I've "bought" more than 50.
Here is my profile in case anyone cares:

Totally recommended.
Goozex eh? Hmm. I've seen the points been referenced on another one, but never actually checked. Seems cool, even though it doesn't exactly say if it's America only. But trading in for points, and only having to pay $1 is just... wow.
Goozex can be used by Canada and the United States. No international support as of yet.
Is this anything like WareZ? I've heard bad things about WareZ
I've not heard of WareZ but on Goozex people are pretty curteous and trustworthy. Occasionally trades do go bad (I've had a few) but the Goozex administrators are very quick to fix the problems and are good at weeding out scammers.