IMO Vegas doesn't know what the hell is going to happen, no way they can trick the public into betting the wrong side. They can only try to make the public feel 50/50 on the spread and think real hard on which side to take. 90+% of public wagered on the Bulls today at -4 and Vegas' estimation was off by 29 points..... clearly public knew what they were doing today.
Houses win because of their juice and money line upsets. Think how it must have felt being the house when 99% of people took LAL money line against Cavs and lost.
It's not like a casino where the long-term probability guarantees house profit, any player can go 100% winnings if they choose the right play.