It's also worth remembering that you have PayPal as an alternative follow-up avenue for many purchases. I've found PayPal works well between honest parties and, as a buyer, I'm quite willing to pay the charges needed to support an assured transaction.
I recently, and for the first time, had a issue with non-delivery of an eBay item from a UK seller. By the time plausibly long economy shipping waits had passed, eBay were no longer interested in helping and, annoyingly, the seller did not respond to messages via eBay or emails, leaving me to wonder if the item was ever really dispatched.
I opened a case with PayPal, forwarded the relevant documentation, and received a full refund in 10 days. Despite being no help whatsoever in resolving the issue, I was slightly amused that it took eBay only hours to close my case with them after being notified (by PayPal?) that PayPal were involved. Very annoyingly, it was impossible to speak to anyone at eBay when the case was open, with the on-line chat "assistant" just clagging out many times with a "no human is available" (or somesuch) message. I have no idea if humans are actually available in other timezones or localities.
So, if you're getting nowhere with eBay, invoke the protection you've paid for as a PayPal commercial transaction user and see where it takes you.
73, Peter.