If GameStop's practices are actually a problem (which still hasn't really been established) then that's merely a symptom of the greater cause. GameStop is playing the game by the rules that were set and it just so happens that the most effective way to play the game involves stepping on the toes of publishers. Fact is, new games don't offer a substantial cut for the retailer. Notice how games work differently than DVDs. You never really hear this about movies. Disney isn't going around complaining about used Blu-ray sales.
I'm not exactly saying that the game market should be a 1:1 match of the DVD market in terms of how pricing works. But if GameStop is so ungodly awful then why aren't more people looking at the things that allow GameStop to work that way rather than just pointing the finger at the company itself?
For a gaming analogy, it's like how if somepony is playing a fighting game and his opponent busts out a game breaking infinite combo and instead of either moving to a better game that doesn't have that kind of bullshit or demanding better from the developers he instead complains that his opponent is being "cheap" when all he's doing is playing the game in the best way it allows. He's playing to win, which is the whole point of a fighting game. It's why banning is so frowned upon in the competitive community and only done in the most isolated cases.
Don't hate the player, hate the game. If there happens to be some fatal flaw in the system that allows GameStop to exploit a loophole then fix the goddamn loophole, whatever it is. And if everypony is content with how the system works (pricing, distribution, etc.) then they shouldn't complain when people, or entities in this case, play the game in the most efficient way possible. You know, playing to win. GameStop is the guy dominating the Street Fighter machine while publishers are the scrubs yelling how throws are cheap and how he blocks too much. Either learn to play the game, move to a different game, or keep losing. Another option, provided you're in the position to do so, is to fix the exploit if there is one or to demand it from whoever is in such a position.