It seems like the vast majority of sellers probably don't in fact know what they're buying isn't kosher. Other than someone asking, "hey what are these?" and Trey educating folks that they're unique to the USMC, 99.9 percent of civilians wouldn't have had a clue. Please don't mistake this as defending selling SGP, because that's not cool, just that we live in a world with ebay, craigslist, etc and some of these sellers may have stumbled on to something by accident. So the question is how do you stem this stuff from being fenced by mil-personal to begin with, before it ends up in the hands of an un-suspecting CIV who doesn't know (and thus isn't thrown under the NCIS bus in the process)?
I know from just visting the surplus stores up near Ft. Lewis that there's some really weird and random parts, gear, pouches, that end up in the bins. Some of it looks like it was dropped off from the armorers, some from soldiers coming back from deployment trying to make a few bucks. When you see shit like BE Meyers target pointers thrown in with the occasional Scout light you're like, "uhhh...time to walk away slowly and get back in the car."
So for all that guy you contacted knows he really had no idea, and him trying to trace back the origin helps companies like KAC, NCIS, etc since they can stem where the parts are bleeding out from. Anyways, just my .2 cents.