My flatmate was ripped off too, he bought a laptop for $1500, it arrived and everything but has really bad water damage (the bottom right of the screen looks yuck and the right number pad doesn't work). Anyway, he emailed him many times and he didn't reply, so he contacted trademe and is now taking this chap to court. This guy has had good feedback with many sales until this trade.
It's not cool when people steal from others, I've had many things stolen from me in my time and it's a crap feeling. Guess you've just gotta be persistent and definitely don't let this guy get away with what he's done.