I sold a 2014 13" MacBook Pro on ebay. Three weeks later I received a message from the buyer claiming that the machine was periodically freezing, required several reboots a day and now wouldn't boot at all. So I accepted the Return. This morning the machine arrived and booted perfectly first try. I rebooted it and ran the Apple diagnostic thing which returned a "no issue found" report. So I took the bottom plate off to see if perhaps the vent was clogged with dust - it was spotlessly clean. So I wiped it and reinstalled High Sierra and then ran etrecheck and Maccheck - both came back with a clean bill of health. I've imported my iPhoto collection and 40,000 emails (both fairly processor intensive). The machine continues to run perfectly. I'm at a loss as to how to proceed. I suspect the buyer changed his mind and thought that claiming the machine was faulty was more likely to get him a refund as I'd put "no returns accepted" on the listing (though that is worth precisely nothing as far as ebay is concerned). Are there any other apps that I might try? Or have the 3 "all good" results said as much as needs to be said and it's just a case of relisting it and hoping for a better quality of buyer?