A number of years ago, I remember seeing a news article on grocery store price errors. It seemed that the news agency found that most grocery stores were 5 times more likely to have an error in their favor rather than in customer's favor. At first glance it would seem that the grocery store chain was willfully trying to cheat their customers. It seems that after looking at the grocery store processes, the news agency figured out that the grocery store chains were much quicker at "addressing" an error when they had undercharged the item. They were much slower at addressing if the error was in their favor, but they would "finally" address it.

So while the grocery store chain didn't "purposefully" try to cheat their clients they had setup a system that was very much in their favor. I have always thought that hotel mini-bars were always treated kind of that way. They aren't "willfully" trying to cheat their customers, but they are aren't in a hurry to fix an error that is in their favor either.