It is my understanding that the 1950s federal switchblade law only applies to interstate commerce. Is that interstate commerce? I don't think it is. If no money is exchanged, and no sale occurred, then I don't think it is.
Also, apparently the federal law was written against the seller, not the buyer. The buyer is safe. The seller, not. He's the "actor." If I bought the knife from Sam Smith in 1998, I'm home free. Sam Smith would be in trouble, though. He sold it to me. Bad Sam.
Over the last couple decades the FBI has vastly exceeded the scope and intent of federal laws like this that were intentionally written with a very conservative eye toward states rights, and intentionally limited to apply only to interstate commerce.
Get Muss Muggins in here and he'll explain how the FBI doesn't build a case to prove a crime but rather *creates* a case to make a crime where one did not exist in the first place by creating an "interstate nexus".
Back in 1977-78 a case was successfully prosecuted in VA where a convicted felon was arrested for possession of a firearm. The court held that the intent of the federal statute was intended to be broad and thus the fact that the firearm had been transported in interstate commerce at some remote time was sufficient to include the necessary element of interstate commerce into the crime.
Unfortunately it's been allowed to creep from there. Fast forward a couple decades and states like Montana allowed firearms to be made and used solely in the state of Montana even if they would violate federal statutes such as the NFA of 1934 if they were taken beyond the state's borders. (The NFA of 1934 has itself been stretched and applied well beyond its original intent. For example look at the NPR issued last year by the ATF using the NFA of 1934 as a basis to require registration or destruction of braced pistols, despite the fact NFA was never intended to apply to firearms in common use (by ATFs own estimate there are more than 3 million of them out there) or to firearms not used by gangs (ATF showed their presence at 2 mass shootings since 2013 (out of 2506 at the time, but didn't show any use, let alone significant use, by gangs).
What the FBI did in states like MT was stretch the definition of interstate nexus by reasoning (and I use that term loosely) that since the steel used in constructing the weapon had been in interstate commerce or failing that, that since the tools or even software someone used somewhere in the process was made or written out of state, that the firearm itself was involved in interstate commerce, thus giving the FBI grounds and jurisdiction for an arrest.
The problem of course is that this makes the interstate commerce clause totally meaningless as everything is involved in interstate commerce at some remote point in time.
The FBI will clearly see mailing a knife back to Benchmade as interstate commerce even if no funds exchange hands. They'll claim since the knife was made in Oregon and sold to someone in another state by known or even unknown means at some remote time in the distance past, it gives them jurisdiction and makes it an offense due to an interstate nexus and interstate commerce.