We study the diffusion of a true and a false message when agents are biased towards one of the messages and able to verify messages. A recipient of a rumor who verifies it becomes informed of the truth. Consequently, a higher rumor prevalence increases the prevalence of the truth. We employ this result to discuss how a planner may optimally choose information verification rates of the population. We find that a planner who aims to maximize the prevalence of the truth may find it optimal to allow rumors to circulate, and we discuss under which conditions this is the case.