Frequent overcharges are not the result of tricks or bad intentions on the part of distributors. The restaurant food purchasing process is an incredibly complex one and simple mistakes can and often do happen if they are not constantly being monitored.
But who has time to constantly monitor - your passion is service and food, not going through invoices. You just don’t have the time to go through every invoice, line by line with a fine-toothed comb to make certain you are being charged the correct amount. To further complicate things, deliveries come multiple times a week, often with dozens of different products, your chefs would spend more time crunching numbers than they would in the kitchen.