> what they are buying is the justice

From The Truth by Terry Pratchett, with particular emphasis on the book's footnote.

> William’s family and everyone they knew also had a mental map of the city that was divided into parts where you found upstanding citizens, and other parts where you found criminals. It had come a shock to them... no, he corrected himself, it had come as a an affront to learn that [police chief] Vimes operated on a different map. Apparently he'd instructed his men to use the front door when calling on any building, even in broad daylight, when sheer common sense said that they should use the back, just like any other servant. [0]

> [0] William’s class understood that justice was like coal or potatoes. You ordered it when you needed it.