You either have to send them a pre paid returns label which you can do via a case if they opened one. or make a seperate payment using the paypal "send money" tab. Use the friends and family tab so they don't have to pay the fee. If you do this it's wise to send the buyer a message so they know where the money has come from.
You must only refund through a case or cancellation if you want your final value fees back and don't want a defect (strike) on your selling account. Did your customer open a case? If not then ask them to do so.
