Usually (from what I've read) covert survellance was set up after suspicions by concerned relatives.

People in positions of trust should be proud that when examined, their performance has been found to be impeccable. If no-one checks, how could anyone know otherwise?

I know this isn't quite the same, but years back, if you went from room to room in the houses of "the upper class", you'd often find small amounts of money (coins) in little pin-dishes or on a shelf. It's not as if they didn't trust "the servants"............ but the servants proved their trust by not pinching any.