So I buy tons of stuff for my tank used. Some would go so far as to call me cheap. When buying anything second hand you are taking a risk. Sometimes you get a sweet deal. Sometimes not. Seems to me he is being more than reasonable offering you a refund. You may have to drive over there to get it, but I think that is more than fair. I understand you being upset, but he is trying to make it right. If this same thing happened on Craigslist the person who sold it could just tell you to bad, you saw it you bought it. On a side note. I don’t really don’t like MP10’s. They make noise and they are kind of an eye sore sticking to the side of the tank. Just my opinion. Hope everything works out for you guys. Happy reefing