One of my friends just sent me an article about G2A and the infamous grey market re-sellers. It's a decent representation of what this issue is and it is a very interesting read. I strongly suggest you read it!

http://tinybuild.com/g2a-sold-450k-worth-of-our-game-keys

(Developer of Punch Club and SpeedRunners)

Enter now!
https://gleam.io/3DMWv/monthly-steam-keys-giveaway-3-hyperactivestudios