Dealers are almost always at an economic disadvantage vs private sales in direct competition. It is part of the cost of being in business.
A certain % of attendees are drawn to the show in hopes of a private sale. This is traffic generated by the prospect of FTF sales to the advantage of the dealers.
If I have a NIB gun I want to sell, I am at an economic disadvantage to the dealers who can buy at a cheaper price direct from a distributer or manufacturer. That is one of the perks of having the license and having to comply with extra regulations.
I think it is a wash. I can sell a few odds and ends, and a couple of guns I don't want with out having to deal with the cost and paperwork a dealer has. A dealer can sell some things at a lower price because his license allows him to purchase in bulk and at wholesale prices, he has purchase options denied to me because he does have a license.
And if you are in the gun business, and you find no economic reason for you to try to sell at gun shows, why are you there? If you are like me, you enjoy the show, being around other gunnies, seeing some new or unusual stuff, you are having a good time, if sales are made it is a bonus. If you are there to make a profit, and with all the economic advantages you gain by having an FFL, you find yourself losing money, because of a few competing private sales, it is your business plan that need re-evaluating, not imposing new federal regulations on private sales. I don't have the FFL, I don't gain your economic advantages, don't force your burdens on to my back without giving me the same benefits you enjoy.