What you also have to careful for is how they'll sell a game that originally had multiple discs, like a soundtrack or bonus disc, and those other discs aren't required for trade ins.
A thing about MGS: Subsistence. When the Metal Gear Solid Collection came out the version of MGS3 that came with it was only the 1st disc to Subsistence. When Gamestop gets copies of the collection in used, they'll split the whole thing up into individual price points and they slap the Subsistence (2 disc version) price on the collection version.
As far as I'm concerned, Subsistence is ONLY the 2 disc version, and yet Gamestop doesn't require that second disc for a trade in.
I've brought it up with multiple employees and multiple locations and I get the same response over and over again. "The second disc is useless because it's the online mode and the servers are down". BULL! That second disc includes the MSX versions of Metal Gear 1 and 2. It's not worthless.
If you're buying Subsistence off of Gamestop's website, expect to get the collection version, and probably no case.
Before they stopped selling PS1 games, I had found a copy of Lunar 2 in their store and just had to shake my head because I knew what the condition was going to be. Sure enough it was game discs only, no case, no instructions, and to add insult to injury the discs had writing on them. Oh, but they still sold it at their "Collectors/supply and demand" price. If Gamestop ran a card shop, they would sell a Babe Ruth rookie card that had been through the wash, torn into 8 pieces, and taped back together for MINT.