I had the same exact experience the last time I sold on ebay, in 2017. I sold an $800 item. One day before the claim window closed, the buyer filed a claim saying it had never arrived and claiming they emailed me several times and I never responded. I submitted proof of delivery from UPS and pointed out the simple fact that I had received no messages from the buyer through ebay messaging. Ebay gave them a full refund…
I woke up one morning to get an email notification thanking me for purchasing a back bumper, a wing, and a few other parts for a 2012 Hyundai Genesis, which I obviously don't have and neither have I made that purchase. The fraudster even put their real delivery address and name less than 20 miles away from where I lived (which I reverse searched and confirmed that the name was associated with that address). I immediately notified eBay about this, they refunded me the purchase, and asked me to change my password. I did all that, removed the perp's address from the account, but eBay didn't have a legitimate 2FA solution, so I was kinda out of luck here.
Lo and behold, the day after, I wake up to info on my account (name+address) changed again. They couldn't change the email, as I have 2FA on my email account, but they did everything they could aside from that with my eBay account. This repeated at least one more time afterwards. By the end of this saga, I just gave up and closed my eBay account after getting my refund.
I just did some googling, and it seems like eBay STILL doesn't support any form of 2FA aside from SMS-based one (which is exactly how, I suspect, they got into my account in the first place, as I didn't get my email compromised). What a shame, but oh well.