I've been going to gun and militaria shows since the late 1970's, first in Montreal, and now in Southern Ontario. My main interest is military firearms.
While there has been the occaisional excellent deal to be had, most of the time I just browse. The internet has become a reliable source for pricing firearms, providing a potential buyer a reasonable "ball-park" cost.
The internet also provides sellers with values, usually from the USA, often for high end, rare, and excellent condition items. Unfortunately, this often means that some rusty, worn out ex-military rifle, is unreasonably priced. A bubba'd Chinese SKS with sanded stock and visible rust is not a $400 rifle.
Frequently, attempts at bargaining with a seller results in being rebuffed. Too often I see a table full of used firearms offered for private sale, priced within a few dollars of retail. These sellers seem to display the same items month after month. Maybe they just show up for the social aspect, and like hauling their wares from show to show.
Accessories, such as slings, magazines, etc. fare no better. Why should I over pay for a military surplus sling, when the same item can be had off e-Bay for half the price, including shipping? Ammo priced within cents of retail?
There are many pleasant and knowledgable folks at these shows, buyers and browsers. Also some unpleasant ones too (death cult goths, criminal bikers, soldier wannabees, nazi enthusiasts, guys that have never heard of deoderant...). Just prepare yourself by doing a little research and setting your BS detector to "HIGH".
I'm not trying to deter enthusiasts from attending these shows. But proper preparation prevents piss-poor, phoney (and overpriced) purchases. I've encountered too many "humped-up" rifles being passed off as original and unaltered. Caveat emptor.