Does GOG let you trade/resale games you purchase with them?
The games are still tied to your account so if you sold the game, you'd be able to download it again... So I think the answer is no.
They do have a money back guarantee if the game doesn't work, but they're going to make you work to prove that the game doesn't work first...
14. But what if a whole LOT of my games don't work? You know: wink, wink. We know that, since we're the Internet's leading DRM-free gaming platform, our Money Back Guarantee offer here is open to a certain amount of abuse. If you're being a bad person who's abusing our trust of you and asking for a whole lot of your games to be refunded and we can't resolve your problems, we'll have to stop offering you refunds.So don't be that guy. No one likes that guy.How many games can you ask for money back? We're humans here, so there's no hard numbers. If it seems like you're exploiting us, we'll let you know and tell you that this will be your final refund offer from us.
Nope, reselling used games is pretty much not a thing anymore on pc. It's part of the "social contract" between pc gamers and publishers - we get cheaper games plus way earlier and deeper discounts and in return the publishers don't have to deal with used sales.
I am the bringer of death. Fall to your knees and beg for mercy... Or give me a sandwich, I'm pretty hungry.