Studies show that people adhere to rules more when they think they are being watched, even if the watching eyes are fake.
A recent stop at a McDonald’s showed this technique in practice. Above the drink and condiment bar where customers serve themselves are the eyes of Mona Lisa. Clearly this isn’t strangely placed art work, it is a technique to prevent customers from over serving themselves.
Me? I still intended to take my five ketchup servings. But I saw the eyes and decided not to be unnecessarily wasteful and took only three (I could always come back if I needed more). I know “the trick” yet I still complied.
Are your customers misbehaving? Maybe a set of eyes will help.