All sportsbooks, Vegas, Offshore or even the average local earn a percentage of the total amount of action (hold) they book. When overhead exceeds the amount of that percentage of the book's hold they begin to lose money. Remember paying winners should be considered part of a books total overhead.
Lose money long enough, regardless of the reason and sooner or later a book will go run out of bankroll and therefore find themselves unable to operate.
Judge Wapner above hit on some of the principal reasons a book can cause their overhead to exceed their win percentage amount and go belly up..
Casinos are somewhat different in that there is substantially less of a chance of a bad run when every game has it's own built in house win percentage. Unless the casino is getting cheated somehow it almost has to make money if there is sufficient volume to create a hold percentage that will cover overhead and still leave a net profit. The trick to winning money with a casino is volume and top notch game secruity.
Bookmaking sportsbettors as a rule is almost always a money maker when done correctly but can fall victim to a bad month or even year if lets for example say an inordinate majority of favorites and overs hit during a particular football season, even more dangerous are games that fall.
There was a period in the early 90s before bookmakers made adjustments that the number three (especially in the NFL) became very risky for the house. Multiple sharp players hitting middles on the key numbers of 3,6 and 7 will put a hurt on a book in a hurry. Volume is important to a sportsbook but more important is the person who is responsible for what numbers they use day in and day out - aka the head lines manager.
wil.