I understand the intent, but feel that there are so many other loopholes that put much worse weapons on the street than a printer. Besides, my prints can barely sustain normal use, much less a bullet being fired from them. I would think that this is more of a risk to the person holding the gun than who it’s pointing at.
I didn’t mention it in my comment but you assume a lot of risk in a private party sale. We aren’t talking about illegal guns but ones that have been registered at some point in time if they aren’t historical.
If you want to sell a gun, you should go through an FFL to avoid liability.