(1) Certified checks bounce
(2) the "refund" you send to him by Western Union doesn't bounce
(3) you will be out that money
(4) you may end up keeping the car in the process, but you're still going to be missing cash.
(5) If he has a shipping service, they already know what it will cost to pack and ship a car, or they can bill him.
(6) I wouldn't even respond, unless it's at the direction of the police or FBI