In the first book, when Conn notes to Nevery that he thinks Keeston is being beaten by his master, Nevery notes that he probably couldn't get away with anything like that. Conn wouldn't let him—he'd leave. When Conn agrees with him, Nevery gets emphatic:
"And that, Conn, is why you are not a gutter boy or a sneak thief."
It's doubly potent not only because it's an affirmation of Conn's noble character, but it marks more or less the first time Nevery says something openly nice about Conn.
Keeston himself is saved from his abusive master to become an assistant to Nevery.