Most market-making books are not in the United States.
In over-simplified terms, there is a four-step process from the creation of each point spread until the game begins. So when you're betting the Chiefs -3 against the Bills, you're also betting against the opinion of thousands of other bettors who have wagered into that line. Sports betting odds like point spreads are like any other 'market.' Betting odds are created through a 'wisdom of the crowds' treatment - bettors all around the world buy and sell the line until it reaches the 'correct' price. There's a common belief among sports bettors that 'Vegas knows' or that oddsmakers are mathematical oracles who can predict the exact score of random sporting events down to the decimal point.
