that's true and the best way to protect yourself as a seller is to add in the cost of insurance (based on the item your selling) and the cost of a tracking label so your adding maybe $2 to your total.
If you're having a lot of problems with people paying with paypal and having incorrect addresses, put in writing that their paypal address must be the same as the mailing address or you will not ship to them, unless they specify it's being shipped as a gift to a gift address, but that information should go in their comments box (about it being a gift) and they should have the gift address saved in their paypal account, there's no reason they can't update their addresses in paypal and this also assures an unauthorized person isn't using someone else's account.