You simply cannot hold the people who bring items to a show entirely on their dime, and therefore help to make that show worth seeing, hostage at that show. If you padlock the exhibitor gate until 4-5pm Sunday and let nobody remove their exhibits, you will have considerably fewer exhibitors at the next show. If you tell the exhibitors this beforehand, you'll have fewer exhibitors for that show.
Even vendors don't want to be forced to hang around if they have a wonderful weekend and don't have alot of their load left or a miserable weekend and not much of anything is moving. When they want to leave, they want to leave, too.
A bonus to entice exhibitors to stay, such as you suggest, would likely have a positive result as far as more exhibitors hanging around. Some might be offended too, as they might see it as a bribe to keep exhibitiors around when they are willing to hang around simply because they want to. Maybe a compromise would be better: a few small prizes/certificates [5 at $25 each, for example] are drawn at random from all exhibitors who, along with their exhibits, are present and accounted for at 1pm +/- an hour or so Sunday that are only good towards the purchase of items from vendors, including food, who are still at the show, with the show organizers footing the bill.
From what I've seen, exhibitors at smaller, local shows don't clear out nearly as early as larger regional or national shows. People that come from longer distances have a longer trip to return home. Some people farm/work/etc., and simply can't spend an entire weekend at a show, even they would really like to.
This post was edited by AG in IN at 19:00:18 07/29/13.