Improper Format deception from the middleman

Hi, everybody! In advance I apologize for my bad English. And now in fact дела:сегодня I offered me an exchange through the intermediary here this person "готоядs" in the morning, and this person - Leon [dota2traders.com] was the intermediary here

76561197988606852 . I wanted to exchange the knife карамбит from cs:go for $200 for WebMoney. We поговрили in 3 in group, later the intermediary assured that everything becomes without deception and I gave it the knife. It took away it, unfriended and left...
Generally, I understand that I hardly will see the knife, but I want to warn other people: don't choose it as intermediary