Have them pay by direct bank wire. A lot of these Europeans are restoration shops and will send out their own driver to pick up the car. It can be very smooth and professional. Just secure the payment as a transfer before you release the car. No pay pal and no cashier check from the driver of the rig that picks it up.
Is this one of the bidders?
http://www.seeland-klassische-porsche.de/
If so, I sold them a car. Really easy transaction.