That's a tough one. Yes, he is definitely responsible and misrepresented it, so he should be held responsible to make it right. The problem is that you accepted it as being ok and already left positive feedback. It makes it harder to go back and say its not ok now. Try to negotiate a settlement. If it was paid for through Paypal, you might have a chance, but with a positive feedback, even that avenue is compromised.
Except for the Automag in front, its usually the man behind the equipment that counts.