My uncle is a retired pilot for UPS in Memphis, he's always told me to ship firearms overnight. Even he knew the possibility exist if left in the terminal. He said overnight shipping doesn't have the possibility to 'lay around' with ground transportation. I've never had a problem in the only 1/2 dozen I've shipped over the years.
Sad to head this story.
I do agree that USPS is the best all around method. As with buying something try to pay with a money order(s) as if someone rips you off the USPS considers this mail fraud and will prosecute on your behalf - so a postmaster told me, thank god I've never had to find out.