I'm not so sure the seller MUST accept responsibility for damaged shipments. That's what insurance is for. If they buyer purchases the insurance and the shipment is damaged they can go back to the carrier for the value. If they don't choose the insurance, the seller is not obligated to refund monies due to the failing of the carrier or the choice of the buyer to not purchase shipping insurance if it is available.
If this were the case, any buyer could simply damage an item they don't like or want and claim it as shipping damage and request a refund. That, at least here in the US, is fraud.