The book "Freakonomics" details a similar bagel-selling system, where they would put bagels in the break room of workplaces, and you would pay on the honor system. After years of collecting data, the owner realized he had been doing a real-time, real-life experiment on how honest people are. You don't know WHO took without paying, but you can tell HOW MANY of your bagels were paid for. There's analysis of how it varies by time of year, type of workplace, etc. Fascinating.