I'm thinking this Paypal/eBay guarantee is that the delivery will make it to you and it's not at all about your being happy with a purchase when your buying from a seller who offers a no refund policy.
IMO it pays to look at a sellers feedback rating (as a seller) and it's kind of a red flag to me when I see a no refund policy.
I've never had a bad experience dealing with a 99 or 100% feedback seller who offers a refund/inspection period.
If negative feedback is found, read it to see what the issue was regarding and keep it in mind.
I think eBay should make it easier to find all a sellers negative feedback rather than scrolling through page after page trying to track it down. But then again they want you to buy so paypal can get their cut.
Paypal states -
"Protection doesn't cover fraudulent charges or buyer remorse. Also, items must be purchased on the U.S. eBay.com website to qualify for eBay Buyer Protection coverage, and are covered for 45 days from the date of payment. Purchases made on Half.com and classified listings on eBay.com are not covered."
Lets face it Paypal is a giant money making machine more than anything else, but it will help you get your money back if your following all their rules and at their discretion.JMO