One of the favorite topics of the anti-gun lobby is the supposed "gun show loophole", which somehow makes it OK for criminals to buy guns, so long as they do it at a gun show. Sounds pretty horrifying, doesn't it? If only it was actually true.
The fact of the matter is that there isn't a gun show loophole at all. Gun sales are under the same laws as all other firearms sales (in states that have not enacted tougher requirements already) -- that is, if you are a firearms dealer you need to run a background check before selling a gun to an individual. If you are NOT a firearms dealer, you can make a private sale to someone else without the need to conduct a background check. But according to federal law, you must be a dealer if you make a living selling firearms.
When the anti-gun lobby speaks of the "gun show loophole", what they are really talking about are private sales. In the United States, it is still legal to own property -- firearms -- and sell that property without government permission. If you want to sell a gun, you can sell it to a dealer, or you can try to find a buyer yourself -- perhaps a friend of yours, or a friend of a friend, or by taking an ad out in the local paper... or by taking the firearm to a gun show.
Since private citizens do NOT have access to the NICS instant-check system brought into being by the Brady Bill, there is no way for them to conduct a background check for a private sale. Thus, they can sell without that check. Otherwise, they couldn't sell at all, or they would be forced to pay a tax to run a check through a licensed dealer -- surely an overly-restrictive process for most private sales.
Part of the confusion stems from the number of private sellers at gun shows. There are often quite a few, and sometimes they have a large number of firearms for sale. Some of these individuals may appear to border on being firearms dealers. Why are they making private sales rather than obtaining dealer status? Because the government is discouraging them from doing exactly that.
It used to be fairly easy (if invasive) to become a firearms dealer. You got yourself fingerprinted, possibly talked to your local police, and filled out some forms for the BATF. That gave you legal license to act as a firearms dealer (and the legal responsibility to conduct background checks). However, in recent years, the BATF has begun a campaign of harassment intended to reduce the number of licensed dealers, and this campaign has targetted first and foremost those licensed dealers without a formal storefront -- ie, those individuals who registered as dealers because they did a large amount of firearms business, but who did not have it as a full-time occupation.
These were the individuals spending a lot of time buying and selling at gun shows -- the "almost dealers" we see today in many cases were dealers before the BATF made it too troublesome to retain that status for something not a full-time occupation.
Sure, there are others making private sales. These are mostly people selling off their gun collection, or that of a deceased relative, or people selling one or two guns at a time and buying about that many back. These people aren't selling lots of guns over time; those selling collections reach the end of their collection and stop selling, and those who are just interested have a low volume overall.
So if there are lots of people making private sales at gun shows... blame the BATF. They don't have to harass people doing the right thing by becoming dealers, even without a standard storefront for their business. But they did, and do... and as a result, the gun show "loophole".