If you are an attendee...
What is it with people who think that it's okay to go around fondling stuff you have no intention of buying just because it happens to be on display? If it ain't yours and you have no intention of buying the gun, keep your grubby mitts off it. Doing otherwise is rude, inconsiderate, and just plain unneighborly. Being offended that someone would actually suggest you do so is juvenile and selfish.
If you like it and have a reasonable desire to purchase it (or one like it), then follow a little personal etiquette and ask if it's okay to handle it.
If you are a dealer...
Presume that there are selfish retards who are going to fondle, drip on, smudge, smash, scratch, spin, dissasemble, and otherwise manhandle your merchandise. If you don't want it to happen, case your guns. If you choose to case them then have plenty of staff on hand handle questions and request to see stuff. One person working a hundred-gun three-table display is not conducive to getting much of anything sold. Be prepared for the dumbest of dumb questions. And teach your staff how to diplomatically end a conversation with a time-monopolizing non-buyer. That person may well come in tomorrow with a roll of hundred dollar bills. Or they may be a prolific poster on many gun enthusiast web sites.
If you're on either side...
Be realistic in your expectations, considerate in your actions, and pretend like you are talking to Art's Grammaw, not like you just crawled from under some rock. A little courtesy, tact, and respect for the person across the table would work wonders.
See, that's not so hard.
Brad