As the title of this week’s episode of Arrow highlights, trust was a major theme in most of the story lines in "Trust but Verify." Moira uses the phrase specifically when talking to Malcolm about Walter, but it seemed to be a phrase Malcolm had used, so I assume she must have learned her lesson from experience.
After a series of armed truck robberies, Ollie and Digg found themselves in a serious disagreement over Ollie’s next target, Ted Gainer. When Digg was in the military, Ted saved Digg’s life, so he had good reason to doubt Ollie’s mysterious book when he discovered that Ted’s name had been written inside of it. The two argued over Digg’s trust in Ted, Ollie’s trust in Digg, and Ollie’s blind trust in his father’s little book of targets.