digital ghost, i'm confused, how does it mean the seller doesn't have to provide refunds?

I'm talking specifically about instances where the seller can prove postage, but uses an uninsured postage option. For example, Click & Send regular parcel is not an insured service, but gives proof of postage. Considering that's all a seller needs to protect themselves, what is the point of SOD or insurance from the seller's perspective?

It's the buyer who loses out if a discretionary (that is, voluntary) refund isn't paid by someone. The PayPal buyer protection policy now states under the eligibility requirements that a buyer is not eligible for protection if the seller provides proof of postage, so if AP don't compensate, and neither the seller nor PayPal refund the buyer, there is nothing the buyer can do to make any one of those parties pay up when an insured service hasn't been used. This might not make much of a difference to a buyer who is purchasing a low-value item and is choosing between a standard letter or registered letter delivery, but it could make a big difference if they're purchasing a higher value item and they're choosing between a standard or SOD parcel service.

Of course, there are many sellers who will refund their buyers regardless of the postage service used, but there are others who will not.