Figure it as a manifestation of human psychology.  About the time that you feel obliged to name your campaign bus the "straight talk express" figure on fraud being an active agent in that individual's operating process.

From the time that "Joe the Plumber" surged on the scene many of us were extremely skeptical.  

One got the feeling from watching Barack Obama with patient courtesy responding to the inquiry from a man who, as it turned out, is not a licensed plumber, is not in a position to buy his employer's business, would not be anywhere close to the threshold of any federal tax hike even if he did, has donated campaign money to McCain and has a federal tax lien against him, that the alleged "man on the street" was a plant.

The body language was unconvincing.  Joe seemed tenuous and his performance appeared stagy as in managed.  After monopolizing a significant amount of Obama's time, an impatient hush could be heard coming over the group of Obama supporters.  One got the distinct feeling that many were skeptical of Joe.