as a Seller, if you choose to sell o/s and you choose to only send by standard airmail, you have to carry the cost of the ''insurance'' yourself.

if you want PayPal Seller protection you need to follow PayPal guidelines
only you know whether or not you sell enough o/s with a good enough profit margin to carry some of the cost, or whether it is costing you too much. in which case you drop o/s selling and rely on the local collectors.