Some faith healers claim to get medical information from God about the ailments of their audience members. Their unexplained knowledge is given as evidence of their divine healing ability, but in reality, they obtain this information through ordinary means.
Peter Popoff was one such notorious faith healer. He was fed information via a radio receiver from his wife, who in turn obtained the information from confederates scattered throughout the audience. Popoff's fraud was exposed on the Johnny Carson Show by faith-healing expert James Randi.
A similar fraud was committed by W.V. Grant, an evangelist who obtained his "miraculous" knowledge of people's afflictions from letters they sent him and from interacting with the audience before his shows. Grant used crib sheets and hand signals from confederates to help him remember details.