Sports books will respond to unbalanced betting by adjusting point spreads to bring betting back into balance. Even if a large amount of money is bet on one side in the form of many small bets, the books will adjust the spread and it would be obvious. Bookmakers set spreads based on getting equal amounts bet on each team and they generally are very good at it. Very rarely do spreads move more than a point or two in either direction, and larger moves often are explained by news that comes out after the original spread has been set (most often an announcement that a starting QB is injured and will not play). Large changes in the spread for no apparent reason would not go unnoticed.
there are a lot of sports twitter people that post what is happening with the betting and how they adjust and what they need. Patrick Everson is one
https://twitter.com/PatrickE_Vegas