The discussion about "agreeing to disagree" assumes ideal bayesians, and the preferred resolution requires that the disputants are willing to spend the time to reach agreement. Prediction markets are one of the mechanisms used by imperfect bayesians to short-circuit the long discussion and find a reasonable compromise. Markets seem to provide good estimates for outsiders to use as the updated value coming out of these disagreements. In a recent conversation with Dan Reeves, I found another reason to doubt that, which seems to play into the discussion started by Manski on what prediction market odds mean.