An NFL example, The Lions +7 at home vs. the Patriots.
On Sept. 23 the sportsbooks across the world faced a huge decision. The Lions were getting 7 points at home, and everyone across the U.S. was betting the Patriots straight, in parlays and in teasers.
Many people were wondering why certain books did not move the number to 7.5 or maybe even as high as 10.
The reason is that sharp bettors would hit “the hell” out of any number over 7. Then, anyone who wanted to bet the Patriots (85% of the bettors) would go to a competing sportsbook and take -7 instead of -10. Therefore, the only betters that would be left would be Lions bettors, taking a GREAT number, and the book would lose a ton of overall action, and $$$, and most importantly maybe those Patriots clients would leave the book.
The sportsbook wants you to keep betting. Sometimes they have to leave a number where it is, and accept the bets, because even if the Patriots end up covering, the sportsbook will definitely get more of your action the next night.
For a reputable sportsbook, more $$$ bet is never a bad thing.
and BTW, the Lions dominated the Patriots, crushing all point spread bettors, parlay bettors and teaser bettors.