I'm no international customs attorney, but I believe any legal risks would be on the part of the receiver, not the sender. I don't imagine the German and US governments are going to negotiate your arrest and extradition over a pocketknife if the importation of that knife violates German law.
That being said, someone in Germany importing a knife might have issues. Trying to nail down Germany's current knife laws isn't easy, different websites say different things. I can't find a definitive source, and everybody on the internet has their own version. In any event, I'd say it's the buyers responsibility to know whatever laws and custom enforcement they might have to deal with.
But on your end, here is what I would be concerned about-
Lets say you receive payment, then ship the knife, and it gets confiscated by German customs, or simply disappears in transit. Are you going to get stuck having to pay a refund? If you use Paypal or similar are they going to take the money out of your bank account if the buyer in Germany says they didn't receive the item they paid for? Can you get insurance against customs confiscating an item (I doubt it).
Shipping across the US is risky enough, but shipping through international customs comes with a whole other set of risks (confiscation).
Here is a link to Germany's customs website. It covers transporting things into Germany, but I don't think it answers your questions. Although it mentions knives it does not get very specific. -
https://www.zoll.de/EN/Private-indi...d-ammunition/weapons-and-ammunition_node.html
And then there's this, German law. Scroll all the way down to the bottom section where it says "Annex 2" to find the list of banned weapons in Germany, it includes certain knives, as well as a specific exemption-
https://www.gesetze-im-internet.de/englisch_waffg/index.html#gl.p0801
I
think the knife you are talking about would be in the clear (manual liner lock?), but I can't say for certain.
My only real concern about shipping knives internationally, and why I don't do it, is just as I explained- the risk of customs confiscating the knife and any hassle and complications it might create between myself and the buyer. I don't use online payment companies, but I still won't do it.