This person usually contacts you on buying something by saying he/she is buying that thing for someone else and wish of payment will be Via Pay Pal.
They don't usually negotiate with you as there are interested not in your car but how to suck of your money from you.

known scenario as following: they will say that someone is going to pick up the item (car, phones, whatever...) and funds will be transferred to your "pay pal account". you will receive some strange email saying certain amount of funds were transferred to your account and you need to pay certain fees to get it.