  A sender has a privately known preference over the action chosen by a
receiver. The sender would like to influence the receiver's decision by
providing information, in the form of a statistical experiment or test. The
technology for information production is controlled by a monopolist
intermediary, who offers a menu of tests and prices to screen the sender's
type, possibly including a "threat" test to punish nonparticipation. We
characterize the intermediary's optimal screening menu and the associated
distortions, which we show may benefit the receiver. We compare the sale of
persuasive information with other forms of influence -- overt bribery and
controlling access.
