Its really not that hard.

Sellers have seller protection if they use the correct postage methods as outlined in paypals policies. In the case of a lost article, they have the right to use seller protection....or not. Its up to them. If they have followed all the rules and paypal incorrectly fnd against them, they have the right to contact the ombudsman.

There will always be scenarios that arent quite black and white, there will always be people that arent aware of their rights and there will always be scammers. There is no perfect system.