Buyer Placed Order but Hasn't Completed Details, What do I do?

Buyer Placed Order but Hasn't Completed Details, What do I do?

A buyer has placed an order from me but has not completed the requirements of the order.
He has set his privacy level to not receive PM's/Mails so I can't contact him.
If I let the order expire and his money is returned, will this affect my User Level/Ranking?
Or is there a way to prompt the buyer into completing the details?