go to return setting at the top right corner of seller central. In there, you'll see 3 Options. I picked the last 1 stating "I will not offer free returns on NONE of my items." So you'll still get to approve or not a return/ refund in the future. Also, not sure if you know, but Amazon return policy is that the customer has 30 days to decided if they want to make a return. once a return is initiated , the customer has 14 or 15 days to actually send the item back. 2 things can happen after this... either they return the item & you give the refund or they never sent it in, therefore, if 15 days pass & still no item & you've tried contacting them through the messages & you get zero cooperation, then it's considered "OUT OF POLICY" ( BEYOND the allowed time frame on amazonamazon's policy). This means you can close out the return, and when it says the reason, which it sends that to the customer aswell, that where you put:

"Hello, Your order # , no longer qualifies for a return due to its Out-of-Policy - beyond 15 days since you initiated your return as per Amazon Policy. Amazon policy states you have 15 days since you initiated a return to return the product. As of today, (enter todays date),15 days have passed since return was initiated & we have not received any return package from you. We even sent a prepaid return shipping label, which has a USPS TRACKING # (enter number) The only activity showing is (date), when a Return Shipping label was provided & a USPS tracking number was issued. This will be closed effective immediate. "