I've been tempted to buy some games with my Bitcoins, but I always end up not doing so, because I cant fully trust anything that isn't steam. How can I know im not getting a stolen/botched cdkey?
Sorry, but that is just stupid. That's like saying: "How do I know my shoe retailer doesn't send me fake Nike shoes?"
There are rating systems on most sites and g2a even offers an insurance for some extra costs.