Posted By:
Scott MI'd simply send an email and ask for a phone number. You could mention that you want to ensure the card is properly packaged and shipped since its an expensive item. Ask for a street address so that you can send the payment via fed ex (they don't ship to PO boxes). Agree to pay for the item to be sent federal express and ask that a tracking number be sent once the package is "in the mail".
I do think asking someone to use a certain vendor is out of line. If I decided to sell a card on ebay from my collection and I'm not a full time card dealer I would not in any way entertain the thought of doing this. And if someone after the auction then said that was the only way they would pay, I'd feel as if they weren't exactly above board.