Here's the thing: You have games that often come in very close to the point spread, and you have at least a couple of bad calls in most games. So, that naturally stokes theories of payoffs.
But consider that many games coming in close to the spread is natural given that point spreads are set due to the relative strength of the teams. And, consider that there are crummy calls because people make mistakes, and like any occupation there are incompetent people in officiating. On top of that, officiating isn't easy. Now, the ref has to make the call in real time from his vantage point while camera angles are many and replays are done in slow motion.
So, some may see conspiracy while others see honest human error. There really is just no way to tell for sure, but I see lots of games where the bad calls go both ways. They mostly even out. And it seems that the fact we have replays in slow motion would really put a crimp in plans to fix high-profile games. My guess is that the mistakes you see in these games are more due to human error than corruption. Game fixing would seem probably more apt to occur in lesser games, especially ones where there is a point spread but are not on television.
I don't think it's widespread, or you would have heard of more officiating scandals. But does it occur? Of course. It's a good bet that no area of human endeavor is free from corruption - not one.
Just keep in mind that no area of human endeavor is free from error, also. The coaches are fallible, the players are fallible, the refs are fallible, and even us fans are fallible.
