Invalid Major new scam!

So today I got scammed, but it wasn't like you're ordinary scam. I saw a gut knife tiger tooth on csgo lounge which was around the same price as my huntsman case hardened, so I sent the guy an offer (http://steamcommunity.com/profiles/76561198250511182) and I waited. I checked back an hour later to see if he'd accepted, and he had, but his knife was no longer in the trade and he had just taken my knife and blocked me. I have no idea how this can be resolved as the steam trade is supposed to be 100% reliable. This guy (http://steamcommunity.com/profiles/76561198250511182) has a ton of knives which you can only presume have been scammed.

Any help is appreciated

 

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