I agree with Drac on this one.  I have placed
several thousands of items on auction in my time
and what I have learned to do is state in every
auction, "We cannot be held resposible for items
lost/damaged in the mail if insurance was not
requested".
They can kick and scream all they want (and many
will), but the minute it leaves your home/office,
the package is no longer within your care and you
no longer have any responsibility.