Originally Posted by
135steward
You're right that a small bookie will lose money if the odds line is, for example, 5:1 and I bet $10k and he only took in $25k in bets. But when a book is handling say $100k/game, he made ~$10k vig off the winners, and paid off from the losers' draw. The only time this fails is when the line is off more than 10%. That, btw, makes line efficiency a big deal for bookies.
When you bet on sports, you're not beating the book so much as beating the guy on the other side of the bet. Books adjust bets by what they bring in on either side. Hell, 5Dimes odds even change in the middle of a bet sometimes.