The scammers use stolen credit cards and pay with PayPal. They say they are buying it for a relative who is currently overseas. They arrange for someone to collect the car and then you lose everything when the owner of the stolen card reports it.
We got two messages exactly like this after we listed our car. Definitely scammers. Have you listed it on a carsales type website? They really appreciate the feedback - they try to keep on top of these things.