Interestingly, one of my coworkers from India expressed disbelief in the trust that cafeterias had in their customers wherein one gets their food from a fridge or hot service and then, with the food in hand, voluntarily walks over to the cashier to pay for it instead of just walking out not paying. He said that system wouldn't work in India (whichever locale he is from) because nobody would voluntarily pay.

I agree with the other child comment to you that such systems only work in a highly trustworthy society.