Big_Boss: Yes but why Steam said that G2play is not legit?
Maybe thei keys are stolen?
Edit: Sorry, wasn't aware that this thread just got necroed. I thought it was fresh. So just ignore. :P
There's many legit ways to acquire games comparably cheap as an individual. You can get them cheaper in a certain region, during a sale, many games are cheaper in retail than on Steam etc. (despite being redeemable on Steam). Some parties acquire games in large numbers this way and then resell them, making a profit. Obviously the publishers and distributors don't like this, though, because ultimately they get a smaller cut. So the terms of service of video games usually prohibit this kind of reselling and that's why services like G2play are considered scammers.
The exception would be of course if such a company has a deal with the corresponding publisher which I think is almost never the case and is nearly impossible to find out without contacting the publisher (unless the publisher has already delivered a public statement on it, of course, like Devolver Digital recently on G2A).
The fact that GOG has no regional pricing and retail games (with very few exceptions) aren't redeemable on here is probably one of the main reasons why these resellers never seem to sell GOG keys.