Same as many others: it's easy for you to know knife laws, customs laws, etc. for your country, but it's not so easy for me to know them for all countries. PayPal Goods is heavily in the buyer's favor and hard to track shipping. Takes too long for you to receive the knife and for deal to be considered closed. Even then I don't trust the 6 month PayPal window. And what if you don't like it, there is some small mark it scuff and you want to send it back? Now I'm eating that cost?
Often buyers say they accept all risk but I've been advised PayPal doesn't accept that, even if the buyer accepts in writing and seen at least one thread with a member commenting in this very thread where they filed a claim anyway and won. So maybe there is PayPal friends but asking to do that is a violation of their terms, and if we are speaking via email you have a record of this to send to PayPal if you wanted to be a jerk. And on principle I don't agree with using it for a business transaction.
Buyers also say they will accept shipping cost. So how does this work? You say you'll take it, then I package my product, take it to the PO to figure the cost, then I message you back: you don't like the price of shipping and back out. Or you don't reply back to me fast enough so I then have to make a return trip to the PO once I hear back from you? With a US Buyer I have the agreed price within a few hours before I ever leave the house.