This has happened to me a few times, but not with knives. So, I send everything with some sorts of delivery confirmation.
Then, if anything happens, the
sender has to file the paperwork to make a claim. Even the US Postal Service is cooperative with filing a claim.
However, don't be lulled into a false sense of security. A claim with any of the big carriers - FedEx, UPS, USPS - takes a minimum of 30 days to process...ouch!
Let's say you paid for the knife
and asked for delivery/signature confirmation and insurance. It ships, but is lost (almost never actually happens within the US). Then, the person you bought the knife from has to file a claim. They still have your money, though. They also no longer have a knife. However, if they do indeed file a claim, then they should refund your money because they will get the claim money.
It's backwards, I know. But that's how it happens.
Anyway, consider these nightmares:
1. A few years back I had a $600 camera lens shipped to my apartment. I wasn't home so the carrier left it with my downstairs neighbor's sister (a black woman! - "yeah I'm Daniel Koster - that big white guy with a beard" !!!



) She ran off with it. I had UPS on the phone and the police at my door when she finally conceeded and presented the "lost" package. What was she thinking?
2. Then, (same apartment

) one day I ordered a 20 pack of high-end SDRAM from a computer wholesaler...valued at the time at $2500. I come home wondering why it hadn't been delivered. UPS said "We delivered it to your back door". Sure enough, I go out back and there is my $2500 box of SDRAM sitting on my step just waiting to be snagged by anyone who happened to walk by! Talk about a heart-attack when I heard them tell me "oh yeah. we already delivered it" !!!
3. I had a small computer retail business (if you couldn't tell already

) and over the years probably had to go through the pain of recovering "lost" equipment that was sent through the mail. It's a real pain in the neck. That was the #1 reason I shut that business down. Shipping costs became to exorbitant to justify having "lower priced equipment".
Not sure if this helps or hurts your thread.
Best wishes,
Dan