As I understand it, at prior Washington State gun shows, there were plenty of private parties selling firearms from their own collection from tables inside the events, incidentally to their hobby, not as a business.
You would be correct, but that is done at every gun show I have attended. We have one of the largest here in Indianapolis with plenty of "private collections." Some of those people are selling personal weapons but many are skirting the law by buying and selling guns for profit. I know one seller was arrested after several convention appearances caught the attention of the ATF.
Selling without a FFL Type 1 license is difficult to prove by the ATF so many people roll the dice because they won't be the one that gets caught.
But every FFL runs a background check or they won't be in business for very long. The ATF does periodically check the books.
I buy and sell cameras inside and outside of shows without a license or background check.
And Nikons don’t even have their own Amendment!