Bookies are not in the gambling business, they are in the "vig" business. Losers pay them 10% vig on their bet....winners collect their full bet, they pay nothing. The ideal betting script for them is equal money on each side whereas they collect a cool 10% of half the entire pool. If there is too much bet on one side, they lay off as much as they can on the opposite side with another bookie who needs the other side.