G2A is dodgy as fuck, yeah. They're essentially just key marketplaces. People buy games when/where they're cheap (either bundles and sales or just in places where games are much cheaper due to regional pricing) and G2A essentially acts like ebay, matching up buyers and sellers.
The extra you pay is to protect you against fraudulent sales and region-locked keys. Otherwise you take your chances.
A slightly less dodgy (in that only one third party is profiting instead of two) is just to buy games from overseas stores like Nuuvem.
It's complicated though. I think we'd all agree that regional pricing is a good thing - games *should* be cheaper in places where incomes are much lower. Taking advantage of that as a person in the first world (and potentially jeopardising it) is quite a twattish thing to do.
On the other hand anyone *should* be able to do whatever they like with software they buy, including selling it.
I'd steer clear and use
isthereanydeal instead.