I don't believe they're 'fixed' but I do believe they will slant it towards one team for ratings.
The two instances that always come to mind are the Seahawks Super Bowl loss and last year's SB where the lights went out once Baltimore got a huge lead. If they can make a call or two that looks halfway legit, I think the refs will make it to help with ratings...but they can only do so much without tarnishing the game.
As for the players being paid off...the only way it would work would be to pay off one of the QBs. And the only QB I ever thought was paid off was the Steeler QB in the SB that one year who threw 2 INTs right to the defender. Forgot who that QB was but it looked real bad.
Neil O'Donnell.....and he made the corner from Dullass that pick sixed him those times a very rich man.....I can't remember his name but he was basically never heard from again. But really who cares, it was Pissburgh vs. Dullass.