The email I got from PayPal looks genuine and gives the status of my refund as "Pending until: November 6, 2019" but I don't see a refund referenced in any of my accounts, not eBay and not PayPal, not even as 'pending'. I've forwarded that email to spoof@paypal.com asking if it's genuine.
The PayPal help website says that 'pending' may be because the seller is making a direct transfer and, if that doesn't go through, the status may change to "cancelled".
The USPS tracking number is stuck at "Your package is on its way to a USPS facility" although that label was created 4 days ago now and the 'seller' stated through the eBay system that he had taken the 289 to the Post Office.
I've tried to contact eBay again but I have to wait until normal office hours.
I'm now near-certain this was a scammer but a very sophisticated one, especially given the PayPal refund email which, even if it's genuine, may not result in me actually getting a refund.