Gamestop is addictive
My boys often trade in their games to gamestop and its a wonderful company. We have the edge card and that has given them extra dollars on items etc. They will trade in their used games and add money to the edge card.
They actually traded in enough games that they were able to buy themselves an Xbox 360 and some other stuff. Which is great as I didn't have to budget for them.
I say be careful because depending on your childs age, they can actually take stuff and trade it in without you knowing about it. I needed to make sure that my 16 yo didn't "convince" his brother (13) that he didn't want that game any more so he could take it in and trade it. That's the one issue I have with Game Stop, the age you can trade things in without parent ok.
Then one night my youngest came to me after being up there with his dad, and I find out that he got a quote to trade in his DS and all the games he has. He could get a Wii with the credit (something he has been wanting). I had to put my foot down and told him no!
Can you imagine a trip from Chicago to WDW with no Gameboy

. I told him there was no way in this current life that he was going to trade in everything especially before a trip like this. I didn't want to hear the boredom in the car
Too funny!!!
So.....go for it, but PLEASE think about the games you buy and don't keep returning. They will change the policy. We have seen it before......