The basic principles of ethos—disinterest, virtue, and practical wisdom—can help an audience assess a persuader’s level of sincerity and trustworthiness. Heinrichs devotes Chapter 17 to disinterest and virtue; Chapter 18 covers practical wisdom.

To assess a person’s disinterest, Heinrichs recommends “applying the needs test” (210). An argument starts with a persuader trying to determine an audience’s needs; manipulation comes into play when the persuader tries to convince their audience that their solution matches said needs. To prevent manipulation, an individual should look for disconnects between their own needs and those of the persuader. If there is a gap between needs, Heinrichs argues against trusting the persuader’s disinterest. Similarly, one should not trust a persuader if they fail to give a straightforward answer should one ask who benefits from their choice.

“Check[ing] the extremes” (210) enables one to assess a persuader’s virtue. Virtue “is a temporary, rhetorical condition—a state of character, not a permanent trait—and you can find it in the middle of the audience’s opinions, or the sweet spot between extreme ranges of a choice” (207). Simply put, a moderate choice is a virtuous choice.