I buy used guns and rehab them for resale and collecting. Here is my protocol for handguns in a show. Carry a small notebook and mark the location in the show of anything that catches your eye. Divide the show up into sections and take little breaks so you don't get gun eyed stupid and confused. It can be dang frustrating at 15 minutes before the show closes to remember where exactly you saw that good price on a used model 28.
1st thing I look for is if it has blatant screwdriver damage on the grip screws, sights, etc. If a nimrod has been screwing with it, you need to take a closer look before taking it.
overall condition of the finish. If it looks like it laid in damp conditions for awhile, you can count on hidden rust in the action.
Handgun bores can be a little deceiving, carry a little borelight in your pocket and illuminate the forcing cone and cyinder walls and take a good look for cracks, swollen metal or erosion.I like to bring a single action gun to full cock and see how much wiggle the cylinder has, also I usually put my thumb betwen the frame and hammer and see how the trigger break is without dry firing. Do not dry fire any gun at a show without asking first, some people get real pissy about even turning a cylinder, so always ask. Don't get pissy, there are lots of tables and lots of future shows, pawn shops, friends being broke and needing money, etc to locate good gun deals at. Don't hurt yourself by overpaying
I have gotten real lucky and scored correct stock grips or sights or original packaging y just paying attention and asking the seller, sometimes you can score a bunch of freebies along with your gun.
Another thing I do is to look at one, if it catches my interest, I will mark the location and go to another table until I see one similar and then start comparing quality and price, etc. Good practice to develop. You occaisionally miss a great buy, but you make fewer poor buys.
My best gun show score was a Mag Na Port arms 4 5/8 Super Blackhawk 44 Mag "Tomahawk" I picked it up for $400 without the box and when I looked in the dealers area, I saw a wooden box and asked what it was, it was the correct box for the Tomahawk and they guy told me, "oh I took that gun on trade and forgot about the box, here, it goes with the gun". I eventually traded that gun for a Ruger Redhawk in 41 Mag. Sure wish I had kept it after seeing how much the Mag Na Port guns go for these days.