How are they in any way, shape or form shady?
While many of their practices I don't have a particular problem with... where do we start.
They treat their staff like shit, even by US minimum wage retail standards. There is a whole subgenre of video and ex employee speaks sites full of ex gamestop employee horror stories if you want to go that one. The management of the things was marginally better (mainly as they were the ones being clueless and making things hard for underlings) but there are no shortage of "I was a gamestop manager and it sucked" stories either.
Their aggressive expansion at points was the big chain approach -- you rock up, do crazy long opening hours, low prices, highly stocked... and don't care if you operate at a loss for a few years, watch all your competition evaporate and then go 9-5 and less than great deals once that is over. While perfectly legal it does leave a bit of a bitter taste, and does also mean local game shops are/were few and far between (they seem to be creeping back in a bit).
Speaking of aggressive they often pushed all sorts of nonsense on people (usually warranties, rewards cards*, their own third party adapters), pushed console bundles hard (if you rocked up at a gamestop anywhere near Christmas wanting just a plain console then good luck with that one as you are going to get a couple of pieces of shovelware with it), and pushed their second hand** offerings on the clueless.
*which I believe as of the other week have been nerfed considerably.
**I really like second hand games and consider it a crying shame that some consumers consider them bad, and find the "it is taking money from the devs" argument to be utter bollocks of the highest order. However to soft talk with fancy sales patter the clueless mothers into buying them when they initially rock up with a new game case in hand... yeah I can see why some have a problem.
The had that thing where they opened and removed download codes from games in favour of their own service.
Some people disliked their approach with xenoblade chronicles. Short version was only after much whining, bitching, pissing and moaning (see Operation Rainfall) did it (and a couple of other mediocre Japanese RPGs) make it to the US (amusing it actually made it to Europe rather than the usual just stuck in Japan). It promptly sold out and became rare and hard to come by. Enter second pressing for which gamestop was going to be the only seller. When it was still sitting in their warehouse they bought their own stock, declared it second hand and promptly sold it at their "it is rare so we charge more" second hand price. Fine by me, and any laws on business I have ever read, but I will note it as part of this.
They have been noted to destroy their old game stock. For the most part it was last gen sports titles which will probably never sell, controllers that might not have met standards and so forth and frankly if you own it then you can destroy it if you want but it rubbed a lot of people the wrong way.
This could go on for a while but those are some nice ones to start with.
When I compare them to epic I can't see why people tolerate gamestop but seem to be ready to go torch epic's HQ (to say nothing of the fellating which Steam gets) -- so far epic have been a bit incompetent in spinning up a service from nothing (though games still get bought and played) and have funded some dev in a few games in return for allowing them the main rights to sell it or the first year thereof (traditionally the main portion but long tail sales are increasingly a thing), all on the same PC without any hardware, extra subscriptions or radical software reconfigurations. About as bad as it gets is as they are Windows focused then the few people doing Linux and OSX builds that went epic dropped those and if you are a gamer on those platforms then you should probably be used to disappointment by now.
100% not buying from EGS, but in general console fanboys seem more tolerant of being screwed over by exclusives (y'know, the whole premise of a console). GameStop exclusivity is why Xenoblade Chronicles (Wii) is or at least was so expensive in the U.S., right? At least GameStop seems to be entering a death spiral, so there's that.
It seems this word exclusive is overloaded.
For many years it meant different hardware would be required, or different hardware within the same class (something could be PC and N64 exclusive, if you were lumped only with a dreamcast, PS2 or saturn you were out of luck. These days console exclusive is often a thing where a version exists on PC, and back when then arcade exclusives or home console exclusives). Moreover consoles I always saw as a way of playing games, exclusives for them then acting as perks for making that particular platform choice. I dislike that model intensely and have long called for the DVD model but different discussion. To say it is the point of such things... that I actually find distasteful.
Retailer exclusive does make various types of sense from broader senses and when said in that but eh.