In Cialdini's Principles of Persuasion, which principle emphasizes the need to repay for favors?

The principle that emphasizes the need to repay for favors is reciprocity. This principle suggests that when someone does something for us, we naturally feel an obligation to return the favor. In social interactions, this creates a cycle of giving and receiving that strengthens relationships and fosters cooperation. For example, if a business provides a customer with a free sample, the customer may feel inclined to reciprocate by making a purchase or by spreading positive word-of-mouth. This principle is effective in persuasion since it leverages a deep-rooted social norm that compels individuals to honor debts of gratitude, making it a powerful tool in marketing and relationship management.

The other options refer to different principles of persuasion: scarcity focuses on the value of limited availability to create urgency, authority relies on the influence that comes from perceived expertise or credibility, and consensus appeals to the idea that people are more likely to engage in an action if they see others doing it. Each of these principles plays a unique role in persuasion but does not specifically center around the concept of reciprocating favors.