Tell the buyer to initiate an INR (Item Not Received)
through ebays system.
When you are notified by ebay, respond to the ebay message with the tracking number to show proof of delivery. Folow the instructions provided by ebay.....if the tracking is complete, you should be absolved.
Do not interact excessively with the buyer. Do not refund unless instructed to by ebay. Make no 'promises' through messaging with the buyer.
