Yeah, that has scam written all over it. My boyfriend is a DJ on the side and gets that type of response all the time. It goes like this (and this could be true wherever payment is involved): They FedEx you a check which is -- oooopppppsss! -- higher than the amount they were supposed to send. They ask you to return the difference. You deposit the check, send them the difference, and then their check bounces. Your check to them was good, but theirs to you wasn't. Happens all the time. And the reason they send it via FedEx is because it would be a crime to do through the U.S. Mail, but they can get away with it on FedEx.
Holly and Murphy