Influence: Science and Practice (Robert Cialdini)
Robert Cialdini is a professor of psychology and marketing at Arizona State University. He's one of the leading experts on the psychology of persuasion in relation to marketing and advertising. The best introduction to his work is this book.
Cialdini's framework is organized around six principles: reciprocity, commitment and consistency, social proof, authority, liking and scarcity. The many examples are fascinating (and distressing, given what they reveal about how we can be conditioned or triggered to say "yes").
Cialdini's work is very well known and every critical thinker should be exposed to these six principles of persuasion. It will change the way you think about all sorts of human interactions.
Cialdini has a brief discussion of the ethics of persuasion in this book, which I'm always on the lookout for, since it's a philosophical interest of mine.