Persuasive communication when the sender's incentives are uncertain

•We study persuasion in a sender–receiver game when the sender's type is unknown.•We find a unique equilibrium in which the neutral sender always tells the truth.•The neutral sender can only communicate low quality levels with precision.•On average the biased sender can persuade the receiver to accept the good.

We study persuasion in a modified Crawford–Sobel sender–receiver game in which the receiver makes a binary decision to accept or reject a good recommended by the sender. The good's quality and the sender's type (neutral or biased) are not observable to the receiver. These alterations yield a simple model and a unique truth-telling equilibrium in which neutral senders who observe different qualities fully separate but can only communicate low quality levels accurately. Biased senders adopt a mixed strategy that can successfully persuade the receiver to accept the good most of the time. When the sender's degree of bias is continuously distributed, a truth-telling equilibrium does not exist. Nonetheless, a partition equilibrium exists for any given number of partitions on the message space.