I was asked a question about gunshows by a person who was going to a big show for the first time and asked for some advice. Tough question, about all I can do is share with others how I do things, many will most likely disagree with some of this.
Try to know in advance what you are looking for and learn as much as possible about what interest you ahead of time, if possible.
Have a budget and if possible take cash, cash talks and many folks, unless they know you, will not take a check or a CC.
When you see something you like on a table take a look at everything else on the table. This will give you a good idea about what the person who has the table specializes in.
Gunshows are a great place to learn about the things that you like, there is a lot of knowledge behind those tables. Ask as many questions as you can, most will be happy to share information.
Buy the gun not the story. This has been said a thousand times but keep it in mind. I remember looking at a rifle in Vegas, the dealer started with how it was a Sedgley and was engraved by someone who worked for Smith & Wesson and did work for Sedgley at night. The rifle was by S.R. Griffin and engraved by Kornbrath, as a matter of fact its on the cover of my book.
When you see something on a table that you want to handle, ask first, always. If the owner is absent either wait or come back, never touch or pickup anything without asking first. We all carry cell phones, so I write my cell on the back of my business card, with a note telling the owner of my interest. Yes, I realize that many do not follow this rule; Im just telling you what I do. You will be surprised how many say thank-you for asking.
Do not ever point out anything wrong with the gun, unless asked. IMO this is the wrong way to do business or get it for a lesser price.
If you find something you want to buy then you can start negotiating the price. I think it pure amateur hour to try to get the price down and when you do walk away and say Thanks Ill think about it or Ill look around and see what else I like. For a lot of people I think that its hard to bargain with others. I always start with something like I like this rifle a lot, are you firm on the price? Once I have negotiated the price down there is only one thing left to do..pay him. If you cant agree on a price that you both like exchange contact information. I normally give them my card and let them know that I have an interest and if they change their mind let me know.
You can have a good time and learn a lot and not buy anything.
Everyone should join in, we have all spent time at gunshows. Besides Im on light duty and have a lot of computer time ;-).