So let me get this straight... you traded in-game items with someone, who promised to send you cash in exchange (like through PayPal or something)?
First of all, in almost all games, that is against the Term of Service, and can get your account permabanned. Secondly, it's like the biggest scam in the book - which is why games don't allow it in the first place. Consider it a lesson learned - don't do off-site trading, especially to random people you don't know.
Normally if you are scammed in game you could report it to Support, but since what you were doing was in violation of the game's TOS, there's not much you can do, since you'd be incriminating yourself.