Great looking truck! $7500 for a 1982 F150 would be extremely high retail, but if it's in excellent shape, it might be worth it...

The first red flag was when the buyer offered you $7500 before even seeing the truck in person. I'm sure the buyer had the opportunity to get the truck inspected by a mechanic before he bought it. Also, most states have an "as-is" sales policy on used vehicles even if there isn't a written sales agreement between the buyer and the seller. Unless you gave the buyer some type of written warranty on the truck, the buyer will need to keep and enjoy that nice truck. DO NOT refund any money to the buyer, because if you do, the buyer will want more refunds in the future and it could imply that you included a warranty with the truck.

This situation has happened to me a few times before and I always said, "You can sell the car for more than you bought it for. Sale is final. Good bye..."