The fact that gambling is prevalent is actually the biggest reason to believe that the games are NOT fixed. Fixed games would kill the profits of the sports books. To see this, you simply need to understand how sports books make money. They do not give a crap which team wins the point spread betting. They set the spread in such a way as to attract balanced action; that is roughly the same amount of money bet on each team. They are not trying to predict the result of the game when setting the spread, but rather the betting public’s perception of what that outcome will be. Assuming they succeed (and they almost always do; they are very good at setting lines), they are then guaranteed to profit regardless of the outcome of the game.
That is because they don’t pay off even money to winners, but rather typically -110 odds. This means that if you bet $110 on a game they pay you a profit of $100, not $110. Consider a hypothetical sports book with the upcoming Super Bowl. Suppose they set some line for the game and attract $11 million in bets on each team. Regardless of which team wins the betting, they then owe the winners $10 million in the winning bets. They have $11 million in losing bets to pay off this sum to the winners. The book therefore makes $1 million off the betting regardless of whether the Chiefs or Eagles win the betting.
Now what could possibly go wrong with this business model? Well two things: either a reduction in betting action or unbalanced betting. Rigged games could lead to either of these scenarios whereas fair games would not. If it became widely known that games were rigged, most people would stop betting on them. Why would you bet on an unfair game? The only people who would still bet would be those who knew about the fix, and they certainly would not be betting equally on both teams, would they? Either way, rigging the games would kill the sports books. The fact that sports books are operating and profitable is a very good indication that games are fair.
I used to think that but there is plenty of unbalanced betting.
Consider the Dec 11 game Houston Texans vs. Dallas Cowboys.
Houston was +1000; Dallas was -2000.
https://sports.yahoo.com/nfl/houston-texans-dallas-cowboys-20221211006/?section=game_odds
74% of the money was bet on Dallas (say $7400)
26% of the money was bet on Houston (say $2600).
If Houston had won (they nearly did), BetMGM would have had to pay out $26000, when only $10000 was bet. As it was they had to pay out $7770 - so they made $2230 for each $10k bet.
Now should you always bet “with the house?” No - I’ve not bet any real money - some weeks you can lose spectacularly if you bet with the house on every game. I’m guessing the handicapper gets fired those weeks.
The fact that gambling is prevalent is actually the biggest reason to believe that the games are NOT fixed.
Back in high school in the 70s, arguments raged about All-Star Wrestling...real or faked. I always asked, can you bet on it?