Plausibly, I think IEM or Intrade could easily be gamed by someone with a big stack, simply for the sake of saying their candidate was “winning”.
IEM and Intrade can change on a dime. They are snapshots for a moment in time. IEM and Intrade flipped and flopped and fluctuated wildly in 2004 when the exit polls said Kerry was going to win. Then it started swinging toward Bush. It was 20-80, 80-20, and then toward the end of the night 55-45 Bush until it became clear it was Bush. If Romney does well in the 2nd debate, you’ll see Intrade and IEM flip in a split second.