Beware! Scammer!!

Hello there i just wanted to keep the community safe by reporting a scammer. We Just agreed to trade on steam,as i contacted him on facebook(there was a group where we trade).So the trade was i had Enclave and Interstellar Marines.He agreed to give GTA IV:Complete Edition Key.I was Suspicious but i did let it go because i knew him on facebook so there was no risk of spamming.(Since i had a key i thought to invite him to trade..in the chat box he will give me key then i will give him the gifts but this was not possible since he had SteamGuard Off)So he didn't agree going first.After a lot of discussion and talking i gave him a idea that i would give him first gift,and then he will hand over the key and then the last gift.He agreed...and i sent him the gift as soon as it was possible(Interstellar Marines)..after 2 minutes i asked my steam key.He Said the gift has not arrived.I saw my inventory and i had already sent him the key.I asked for the key but before i could type he went offline and didn't appear again.After sometime he wasn't in my friend List.I was very but not too much since i had won the game in a GiveAway.All i wanted to do was inform you guys to stay away from him.
His Steam Name:
Jason-Bourne
His SteamId:
http://steamcommunity.com/id/Ok9
Facebook:
https://www.facebook.com/X.Youssef.adada.X

You may see his games he has Interstellar Marines in his games
Check http://steamcommunity.com/id/Ok9/games

Please Help Me....

ONE MORE QUESTION!
What Is Impersonaters?