To give the short answer to the question: No, you cannot.
The reason for this is because shipping carriers provide a service, to send your package from one destination to another within a specified timeframe. When your package enters the delivery “stream” then it considered shipped and the carriers have done their job, so you cannot get a refund on that label, even if your customer does not want to keep the item delivered to them.
Un-scanned labels that never make it into the delivery stream are eligible for refunds. However, if a customer receives your package and realizes he or she doesn't want it, then you cannot get a refund on the original postage and you will typically have to pay for a return postage label as well.
The only way to avoid paying for return postage is if the item shipped was delivered to the wrong address, and whoever received the package did not open it and writes "Return to Sender" on the package. This is only designed for people who received something they never intended to receive, and should not be part of your store's return policy.