There is nothing that eBay or PP can do; they have no idea if you have sent the item, and you have no proof of sending it.  PP offers seller protection to sellers who satisfy certain criteria = send by online trackable option.

That's really what it boils down to. It's explained on the PayPal website that they offer seller protection when you either ship via a trackable method or ship with a method that obtains a signature on delivery. For the most protection, I recommend the latter.

If any item is not worth the risk of losing the funds (and the item), you should automatically ship it with SOD. If possible, try to factor that in before you list the item so you're covered for the additional cost.