Dealer? or private indivdual?
As I understand it, the BATFE still uses the terminology "engaging in the business" and the crime is doing that without a license. I know several invididuals who have large collections who attend several shows yearly, and sell parts of their collections at them.
They use the money they make to buy their groceries, pay for their hotel bills, and yes, on occasion buy other guns for their personal use. And later, those guns may show up on their tables when they are tired of them.
Engaging in the business is interpreted to mean buying guns with the intent of resale. It isn't about the number of guns you have for sale, or how many shows you sell at. You are still allowed to sell your private property as often and in such volume as you wish.
Making a profit on your property is nice, but does not figure in the definition of engaging in business. Your intent is to profit, sure, but you could be found to engage in the business, even if you sold every gun you bought for a net loss.
The nice thing about gun shows is the oddball, rare, antique, out of production stuff that shows up there. That and the fact that there are still people willing to buy, sell, and trade guns. For me, the FFL dealers who drag out their inventory of black rifles and combat tupperware are just taking up space. But they serve an important function for many other people, so I don't mind.
As to the idea of mandated background checks on private sales, it is, like communism, a good idea in theory, but not such a good one in actual practice. It is, in effect, an unfunded Federal (or state) mandate. They are requiring you to act as an agent of the government (which FFL holders are, due to the license), but requiring you to pay for it. My opinion is that if the govt requires it, they should pay for it. I feel the same way about auto insurance, but haven't been able to get anywhere with that one, sadly.
As for the risk of criminals getting guns at gun shows, liberty doesn't come without risk. For my freedom from govt interference in how I conduct my personal affairs, I will accept the fact that a small percentage of people will abuse that freedom.
I would rather have a justice system that caught criminals, took them off the streets and kept them off the streets over a system that denies me the ability to buy and own guns because others misuse them. Unfortuantely, currently, we have neither.