Trust him not with your secrets, who, when left alone in your room, turns over your papers.

Character shows in the moments with no audience. Somebody who reads what is not theirs while you are out of the room has told you exactly how they treat information, and no assurance afterwards outweighs the demonstration. Small breaches are not small; they are the same behaviour at a lower stake. People stay consistent in ways they never intend to advertise.

Watch what people do when nothing is being observed and no score is kept. How they treat a waiter, whether they return what they borrow, what they do with a message not meant for them. Then decide what to hand over, and give less to whoever fails the small test.