Old school here....hate PayPal to death.
I've sent the knife (knives) via USPS or UPS insured with a DC or Signature Required.
Upon receipt of the M.O. I wait until confirmation via email/text/phonecall that they are indeed happy with their purchase.
For example, I just sent a knife to AZ today. Emailed the tracking number and already received a response that they are tracking it.
Once I get confirmation they received it and it passes their "muster", I cash the M.O. and all is good.