I think things here are a little different, only because you are dealing with an individual.
Many times we do not know who we are dealing with. It is as easy for me to say I din't receive the item as it is for the seller to say he shipped it.
Many sellers now post that they accept no responsibility if the item is lost providing you do not ask for the optional insurance.
In this case the envelope arrived without the contents and it is a CLEAR case of improper packaging.
The seller SHOULD replace the item.
The buyer paid the requested shipping fees. As a result of this shipping fee payment, it is reasonable expectation that the item be properly packaged