I got several of these scam emails from supposedly different people, all giving different reasons why they couldn't come and view the car ("buying for my daughter, I'm on a navy ship, etc") but would still be willing to pay the full price via paypal.
The first one looked suspicious, so I did a quick google and found several reports of the scam.
After rejecting the first "offer" I still got more emails the same.
I've only got these when advertising on Autotrader.
I would never accept paypal for a car, even if the person was legit.