Deception in the marketplace, the chief topic of Michael John Pettit’s work, offers a fascinating gallery of rogues along with the legal, bureaucratic, and scientific actors who worked to try to identify, classify, and suppress public dishonesty. Pettit focuses on the United States from the Civil War to the Great Depression, a distinct period, he suggests, during which new forms of deception and new strategies of control were linked to a vast expansion of commercial culture. Ranging through an impressive variety of sources, his paper examines the legal effort in the late nineteenth and early twentieth century to protect consumers from products that were marketed in such a way as to create confusion with a better-established product. In fact, however, as he persuasively argues, this was mostly about protecting established brands against upstarts and imitations. The paper also investigates the marketing of psychology, which came before the courts peddling objective methods for determining when consumers were being misled. However, as petit explains, judges generally rejected this form of expertise, preferring their own untutored ability to recognize a deceptive product over the pretensions of science. In Petit’s hands, this rebuff of legal psychology becomes a revealing episode in the history of social science in the public domain, suggesting the limits to the authority of experts before a professional public.