Ancient historians and truthfulness

Came across this quote in Josephus today: "while veracity is incumbent on a historian, he is nonetheless at liberty to refrain from harsh scrutiny of the misdeeds of individuals, not from any partiality for the offenders, but because of his own moderation" (339).

Mason in his notes (p. 138) also quotes Avenarius (1956), saying that while the profession of truthfulness was everywhere among historians, "Nevertheless, the vast majority were not conscious of the obligation that they undertook, since the assurance had degenerated into a rhetorical flourish."