At a guess, he wants to return something he bought.
Your best bet is to ask him.
Because the safest way to return a purchase involves expensive Delivery Confirmed service, it is best to keep the unhappy customer sweet. You are not required to refund the return postage (although if the problem was caused by your actions, it would be a Best Practice). Avoid having a problem turn into a Paypal or eBay Dispute which will hurt your seller record.
