CallMeAl I've always been under the impression it is the sender that has to make any claims. Esp. in a case like this where the buyer never received it. You are protected no matter, for the full amount. If he screwed up on the ins. amount, it does not affect you; you either paid by CC or PayPal, or such, and will get all your money back. Besides, you did not buy the ins., the sender did(or didn't), so you'd have no claim, if I understand it.
Personally, I'd ditch this seller, permanently. Like a black cat. 😉