For the 2nd time in a few weeks, a customer has requested a refund stating the thermometer I sent them arrived broken.  Previously I wrapped them in cardboard and then inside a bubble mailer.  After the first refund I started putting thick foam around the tube area as well as marking the package fragile.  I have seen the contractors at Aus Post routinely chucking boxes into their vans, so what more can I do?  Even a cardboard box isn't going to protect things if the delivery guy puts really heavy stuff on top of it, not to mention hugely increasing the postage cost.  

Any suggestions would be most welcome.

Thanks.