That doesn't make any sense. Why would you post this on THE bitcoin forum if you aren't selling them for bitcoin?
Also, i don't think this is legal... I heard Steam bans accounts for purchasing keys this way.
Please, inform better to say things like that. Because you scare the people with a lie. Banned to trade games for keys? When you find the source of that info, paste it here, if not I would appreciate so much if you can rectify it, because as I said, it a lie without any valid argument.
Check the trade F.A.Q of Valve.
If I post here, its because I saw other threads with trades by other ways than bitcoins and I thought its a good forum to create this thread. If I cannot do that, report to mod and if they think that really I cannot post here, delete the thread of course, Im not going to go counter the rules.