This paper frames Conrad's practice of verisimilitude as a technique of securing the reader's trust. Understood in this way, verisimilitude emerges as a vital term in the equation linking Conrad to modernism, on the one hand, and to the mass market, on the other. I draw on Georg Simmel, H. G. Wells and other contemporary sources to establish the importance of trust and trustworthiness to literary writers at the dawn of mass society. Engaging with recent critical studies of professionalism and modernist self-fashioning, I examine how professionalism functioned in Conrad's self-presentation, but also how the technique of verisimilitude that he developed in Lord Jim surpasses the rhetoric of professionalism: Conrad deployed verisimilitude in Lord Jim as a substitute for certification.