I have always asked before picking up a gun from a table. If I am just checking markings on it, I might roll it over with out asking, but it is still technically on the table when I do that. Other small things, like reloaders, dies, etc, I usually dont ask if they are on the table, unless the owner is standing right there.
Now, on the other side of things, when I am set up with my leather gear, I dont mind people picking them up. BUT when they take out the dummy 1911 and try to shove the dummy XD into the 1911 holster, even though they are marked as to model, I get a little agitated.
I do have a few old original holsters on my table as a display as well. Those I try to keep to the back of the table, or on a rack where they are not handy to grab. Some things are NOT for sale at shows, but are used as examples instead.
As for losing merchandise at shows, I have not yet, but Run N Iron has lost a few items over the years. I think a scope or two was in the mix, but I dont remember any firearms missing.
RT