Trading in board swaps & repros to Gamestop for quick cash is 100% wrong. Anyone who says otherwise is just a greedy jerk.
No one is required to accept Gamestop's prices. You want more money? Sell on Ebay, sell on a forum, have a damn yard sale. Gamestop, despite their shitty values, does provide a service- they don't say no.. You got a handful of disc-only, scratched-up old sports games that people online don't think is worth the cost of shipping? Gamestop'll take 'em. You'll at least get a candy bar out of it. Choosing to rip Gamestop off gives them a good reason to start saying 'no'. Wouldn't it suck if they implemented a a new policy where they can turn down trades? Imagine being a kid hoping your old boring games will get you just enough for a new fun game, only to have a lazy cashier decide they don't want to process your trade in? I mean, think about it- you wouldn't bring a bunch of rare games to a good game store, they'll be suspicious. This is a thing becuase Gamestop won't say no.
As for not testing games- we all know Gamestop doesn't test everything anyway. They've always used their customers as their test base. If you do this, you KNOW for a fact your fake game is going to get bought. "oh, they can just return it." Unless, you know, a friend or relative picked it up as a present and the return window's closed by the time you get it. Not to mention the opportunties that person will have to pass for the game they want becuase they think they have it already.
You can take advantage of Gamestop if you really want to- you can watch trade-ins, wait for a raised value, use a promo at the same time- I've seen guys get their trades valued over the cost of the game on the right day. There's often games that GS sells for notably less than Ebay, if you can find one in-stock you can flip for profit. I share my Pro Rewards membership with my fiance's family- techincally against the rules, but they'll never buy one- now they get the discount & I get the points. I spend them on renewal certificates so I don't have to pay out of pocket. And Gamestop technically gets more sales now, since they can do better there than online.