PayPal dispute res (ya gotta log in) https://www.paypal.com/uk/cgi-bin/webscr?cmd=xpt/customerservice/EducationSellerOverview

"Try not to enter communication with the buyer under the assumption that they are acting unfairly or unreasonably. Make it clear that you see the situation as solvable and include some suggestions about how you would like to resolve the dispute.
Because the funds associated with a disputed transaction may be held until the situation is resolved, it is in your best interest to communicate with the buyer as quickly as possible."