Have an idea what you want and what they sell for. Know the range you are willing to pay. I don't go to the Lex shows as I despise really large crowds and no one knows how to drive up there. I head to the one in Somerset as it is a little closer to me and I"m familiar with the area. But a show is a show is a show. They are full of dealers and traders and people skulking around outside. Make sure you have your ID so if you buy off a FFL dealer you can do the paperwork.
Lot of people are trying to capitalize on the run on guns these days. But way I see things is things are only worth what another is willing to pay for them. I'm not sure silly is a term you might want ot use for the way things are right now. People are nervous and with a reason to be I can't blame them. No one really knows what's coming down the pipe or when. Many people that have never owned more than a hunting rifle (if that) are going out and buying up what they can before it gets banned. Will it? Can't say, but it looks like it might be rough for gun people before too long. I don't buy into the craze but I"m one that likes to keep things stocked in a manner that I don't get caught up in situations like this. I never put things like my or my family's protection off.
WE all can't be ants though. Someone has to be the grasshopper.
Anyway, if you have an idea what you're looking for go to gunbroker's site
and look at prices and see what they are selling for. Then you know about what to give. Expect to haggle, but I'd say there's not a whole lot of wiggle these days with the huge run on impulse shoppers.