In my decade plus of using PayPal they have always sided with me when I provide proof through screenshots, and detailed explanation of events (I've filed less than a handful of claims in that time, but all have been expediently resolved in my favor). As long as you are sure that the knife you purchased is legal to own in your region, then there is no reason they should all of a sudden decide to cause problems for you if you file a claim. But make sure that in your claim you have quotes of the relevant knife laws in your area, links to the government site where you found them, and screenshots of the conversations you have had with the maker, including his false or misleading statements, and your evidence that they were false or misleading. In addition, you should show proof that you ran into a wall when you tried to amicably sort it out with the seller first, as the PayPal process requires you to at least try to resolve with the seller before filing any claim against them.
