(sighs) first of all, discussing it here achieves nothing. If (and only if) you have proof then you should report him here and even then the best you could hope for is get his SteamTrades account suspended. You could also try to report him to Valve, but again you'll need proof and again you won't get anything back. And don't bother with SteamRep, they are useless.
Here is the proof can this suspend his SteamTrades account
http://imgur.com/21WGtse http://steamcommunity.com/profiles/76561198048094247/ http://www.steamtrades.com/user/id/76561198020696458
you posted the profile of cg, the steamgifts/steamtrades owner. he certainly didnt scam you. i guess you fell for an impersonator.
This (useless) thread is a duplicate and I already warned you that's against the rules, close one of them. Or better yet, close both already.
I am new to this forum and wanted to trade couple of my Bioshock infinite keys gave the code first cause this guy has +20Rep
http://imgur.com/21WGtse http://steamcommunity.com/profiles/76561198048094247/ http://www.steamtrades.com/user/id/76561198048094247/