One of the first things I teach students is how to look at a gun. The person with the gun checks to make sure it's empty and hands it to the person who wants to look at it. The person receiving it looks to make sure it's empty. There is no exception to this rule.
Something else to look out for at a gun show is anyone picking up a gun with their finger on the trigger. When I see that I move away. My rule is finger off the trigger until your sights are on the target. If you want to try the trigger make sure the gun is pointed in a safe direction.