I bought an ESEE 4 at a gun show and it was about the same price that can be found online.
To be successful at one of those you need variety, as addylo said. I always see a wide selection of wares, from CRK, Emerson, Spyderco, and Benchmade all the way down to the lesser brands like Mtech and Smith and Wesson knives. Based on what ive seen id bet they are more successful at selling the latter in terms of volume. Knife nuts arent common at those events so most people are drawn to cheap.