1. The Rule of Reciprocation: “We try to repay in kind what another person has provided us.” People tend to return a favor, thus free samples in marketing. The good cop-bad cop strategy is also based on this principle.
2. Commitment and Consistency: If people commit, even if only orally, to an idea or goal, they are more likely to honor that commitment. Having established that idea or goal as congruent with their self-image they tend to act in accordance with that image. Even when the original incentive or motivation is removed after they have already agreed, they will continue to honor the agreement. In car sales, say, suddenly raising the price at the last moment works because the buyer has already decided to buy. Get people to rewrite their self-image and you get automatic unenforced compliance. (See cognitive dissonance.) Once we make a choice or take a stand, we experience personal and interpersonal pressures to behave consistently with that commitment.
3. Social Proof: People will do things that they see other people doing. Viewing what others around us think is correct powerfully impacts what we end up deciding is correct. (Asch conformity experiments.)
4. Authority: People tend to obey authority figures, even when asked to perform questionable acts. (Milgram experiments in the early 1960s.)
5. Liking: People are more easily persuaded by other people who they like, respect, or look up to. (Tupperware parties: guests are more likely to buy if they like the person selling it to them.) We prefer to say yes to the requests of people we know and like.
6. Scarcity: Scarcity, real or perceived, will generate demand. Thus limited time only sales or unique, one-of-a-kind labels.
Based on: Wikipedia and “Influence: The Psychology of Persuasion,” by Robert B. Cialdini, Arizona State University