Since my last (still ongoing) fiasco with USPS I've gotten so paranoid about shipping stuff now that I've started photo documenting the process. I take photos of all the contents, including photos of the stuff in the shipping container. Make sure you save any and everything that proves value!
When I first started dealing with Paypal, I was super paranoid too.
Photos are almost free now, just takes time and computer storage space.
I take photos of the items themselves, the items in various stages of packaging, the items with the shipping label together, the package showing all 6 sides of the package with HUGE shipping labels
(It's hard for a sneak thief to quickly readdress a package when every inch of the package is covered in original address labels and fully taped over.) and so on.
I also take the camera to the PO and take a pic of the package with the shipping receipt, sometimes with the clerk and the package too.
and a close up or scan of the receipt too.
The post office folks think it's odd, but they just smile for the photo now and don't complain.
I send some of those pics to the customer while it's shipping too - communication is crucial and it keeps them happy until it arrives.