Partway through Haunting of Harrowstone, and my players keep using the spirit planchette. Unfortunately for them, however, it's 0-3 for telling them anything truthful thus far. When asked who was writing in blood on the memorial, the planchette fingered both Father Grimburrow (which led to some amusement as the rogue followed Grimburrow and his acolytes around as they handled suspiciously collected various risen corpses for re-sanctification and re-burial) and Kendra. They final caught Gibs on one of his nocturnal jaunts, but because of the doubt planted in them by the planchette, they think that it just happened to be Gibs that night. Upon asking the spirits who had possessed Gibs, they decided to again misdirect and only replied "the tyrant". Now the players think that the Whispering Tyrant is much more directly involved in Harrowstone, and as a devious GM, I couldn't be happier.
What whoppers have the spirits told your players via the planchette?
I'd change the thread title so that you don't give away that the planchette can lie.