Cyraxpt: What is his gog account? Was the trade made here?
Ignatia1821: I don't know yet. My post here requested contact here or on Steam. He happened to choose steam, so I only know that username.
Then that's the problem, this thread is for gog forum scammers so that we have awareness of who they are, if the deal was made on steamgifts then it's there that you should expose him as a scammer, at least people will know what to expect from him.
As for a solution, i don't think there's one, i'm guessing that you got your The Witcher 3 from a graphic card promotion, if you had bought the game maybe you could chargeback and the guy would have the key revoked...