well, try to talk to him, if he blocked you or something else
Go to : http://forums.steamrep.com/
and report it there too, but you need to proofs like screen shoot, etc
Do you have a screenshot of your conversation and proof that he scammed you? It could be an impersonator of him that scammed you. Since you are new on Steamtrades, you are an easy target for impersonators, and they like to use high rep traders to get new traders on here.
SO someone just linked me this thread - HOW did I scam? because Im quite sure I do not know you ;-)
EDIT: I guess I do know you, you added me 12 hours ago but we havent even spoken - so whats the deal?
If you traded with someone who ahs my nick (and I doubt I have impersonators as I do not really sell stuff) then show us convo history/trade history etc. Then we can find out who you traded with and deal with it.
Go to: Inventory, click on "more" then go to "view inventory history" and either post it here or send to me - because I want to know if I have the impersonator and I sure as hell don't have a trade with you there.
PROOF:
Seems the issue is resolved, support ticket logged, -rep removed and scammer reported. if anyone has a free second report him please:
http://steamcommunity.com/profiles/76561198127944002
With previous bans should be a quick fix ;-)
This guy has 381 Positive Replies and then he scams me.
Heres his profile http://www.steamtrades.com/user/tkrysiak/page/1