Frankly this sounds more like an issue with USPS and the seller. I am neither anti-eBay nor pro-eBay. It's a valuable service, it's low cost compared with other options and I haven't had many horror stories. On the negative side, I think it's appalling that they're allowed to have any interest in craigslist and the relationship with paypal offends me. So I do think I have a balanced view, and I'm not sure eBay can be expected to get involved after delivery. At some point eBay needs to be able to say the item is delivered, it's out of our hands, and I don't think it's fair for them to demand the seller pay to ship again when the seller is not at fault. Your beef is with USPS.

Now the piss poor service standards and the lack of liability and responsiveness by USPS are absolutely infuriating, especially when the employees are paid well and treated well as a union quasi-governmental service. If you think contacting a useful human at ebay is hard, just try contacting one at USPS!!

I would offer to eat the shipping and ask the seller to do the right thing. It sounds like the relationship has already been compromised by the prior mediation.