I prepare a bill of sale in advance that includes every part of the description, condition, origin, service history, etc. in the ad and require the buyer to sign my copy - prevents "you never told me" complaints. For race vehicles: "not legal for street use, cannot pass inspection".
Anyone paying full price is a scam.
Any overpayment with a refund is a different scam: "I accidentally bought the money order for $500 too much. Wait 3 days, then send me your money order for $500 and I'll be there Tuesday to pick up the car". He doesn't want the car at all - he wants the $500.
Anything but actual U.S. currency is dangerous - including certified checks and wire transfers.
If during business hours, take the buyer and his money to your bank and have the teller put it through their counterfeit-detection counting machine. I just got a bad $50 selling a bike - which the bank seized.