My advice is get on the phone with an ebay rep asap, not through chat. Actually ebay will call you. Be super nice with the ebay rep, kindly ask them to pull up all the emails with the buyer so they can see exactly what is going on, they will see the buyer admitted they did in fact receive the item. Ask them to make notes so if you have to contact ebay again the next rep can view what the 1st rep said. Tell them your concerns, ask them what to do. This is basically covering yourself. the questions you're asking here, ask the ebay rep. Thats what they are there for.
I would also contact usps, actually go down to your local post office where it was sent out of. This may not be the closest post office near you, for example the small post office down the street is useless and cant do anything, I have to go to the larger post office the next town over where all the mail gets processed through.
You will be surprised what info is saved with that tracking number. Ask for the entire printout of that tracking number. Whenever it gets scanned the exact location is uploaded and saved, the actual latitude and longitude. This info does not show up normally, its kept internal and a post office manager has to look it up. This is where getting friendly with the local post office comes in handy, they may not just hand that info over to just anyone but if they know you they will most likely give you anything.
I've gone through something similar selling an item, buyer wanted to return it and after i sent a return label i didnt hear back. but they did finally send it. if/when you receive the item back look it over and make sure its exactly in the condition you sent it. if so issue the refund.
