[Eric72]

You may want to video the box opening when your package arrives.

Alternatively:

If you're signing for it at the Post Office, perhaps you can have the Postmaster witness you opening the box. Tell him/her you suspect the sender may have sent you an empty package, or something with only packing material and no actual contents.

It becomes infinitely easier to pursue a remedy when the Post Office verifies the package was empty at the time of receipt.

Just "thinking out loud" here. Good luck with everything.