Hard to imagine these sites are "independent".  Why would they be?  They have the power to form a narrative, and that is valuable.  If there is value, it can be paid for.  

Consider "journalism".  Your first lesson in journalism school is to journal.  ie who what why where when?  But instead of recording the narrative, they now form the narrative.  One of the only true jouranalists that told the truth, wikileaks, had its leader put in jail.

You have to imagine the pollsters and prediction sites are similar.  Prediction markets are a bit harder to game because of the liquidity.  But at this scale they have alot of margin, and its not as liquid as sports finals.

I'm not saying that everything is rigged.  But I am saying that there is alot of rigging going on, and assuming independence is not a rational starting position.