For security, insurance and other reasons, strictly control access to your show floor during set up and tear down as well as during non-show hours on show days. Establish procedures to account for everyone who is allowed on the floor. Exhibitor personnel must wear a clearly identified EXHIBITOR badge that is color coded to immediately distinguish it from that of regular attendees.
Issue set-up people large, numbered badges and record each person's name and number. If a problem, such as hassling an exhibitor occurs, the badge number can be used to track down the offender.
Note: Many times simply the appearance of strict security will deter the bad guys.