Do dealers at FUN show only sell or also buy coins? Can you walk in with some coins you are willing to sell?
Very few dealers can exist without buying coins. My guess is you would be hard put to find a dealer at that show who would not also buy. However, the dealer may not be interested in your particular coins be it because of price or variety.
Of course, all depends on what your selling . I've seen someone offer a hundred thousand dollars for a 1969-S Lincoln DDO-001 .
Every year, the Jacksonville (Florida) Coin Club rents a bus and schleps many members down to FUN, and every year they say it's better and better. I've only been to two, early 1990s. Next year would have been my 60th year in FUN, but I dropped out when I left Florida, 12 years ago.
Sure, almost all the dealers will be buying (that's how they get the stuff to sell). But don't be offended if a dealer isn't interested in what you are offering. Sometimes it may be material they aren't familiar with, sometimes they may already have enough of that type of thing, sometimes you might want too much money for it, or sometimes they may just not like what you've got. Sometimes, I've had to go to half a dozen dealers before I found one that wanted what I had. As always, premium quality, rarity, strong eye appeal, and originality are going to sell better. Its just like you when you are buying.