If you are going to bet big, then you need to be aware of not only getting the best odds but also the smallest margins. Bookies earn by betting with greater margins than the punter. On some markets, bookies will try to price up the event so make money regardless of the outcome but in some sports, this is not possible so essentially the bookie is betting against the punter.
The formula for working out the margin on a bet is quite simple.
Margin = (1/a) + (1/b) + (1/c) – 1
where a, b and c are the odds in decimal of the outcomes.
So take a game, Spurs vs Liverpool at White Hart Lane. At Bet365 the odds are 2.3 home win, 3.4 draw and 3.0 for the away win. Doing the maths, it works out that Bet365 make a margin of 6.22%. Thats quite low but there are other markets that are even lower.
On the Asian Handicap, the odds for Spurs -0.25 is 2.05 and Liverpool +0.25 is 1.85. Doing the maths for this, you can see that the margin on an Asian Handicap bet at Bet365 is 2.83%. More than twice as good as the 1X2.
With this knowledge, you are almost always going to be better betting on Asian Handicaps rather than 1X2. There are some rare occasions when the 1X2 is better but its rare and more often than not, the exact same bet on the Asian Handicap is better value than doing it on the 1X2.
Bookies get away with more margin when there are more outcomes to an event. Horse racing has a huge margin as there are many outcomes. Events like the Grand National can have margins of 40+%. Correct scores, first goal scorer and scorecasts all have high margins too. If you are serious about betting, probably best off giving these a miss.
In terms of overall value, rugby handicaps offer the best value. A lot of bookies have even money on both sides of a handicap and make a small margin on the draw. The thing is, not all bookies have the same line.
For example South Africa vs USA. South Africa – 40 is even money at Bet365. USA +41 is Even money at Ladbrokes. Say the game ends 40 – 0 to South Africa, the bet at Bet365 loses but the Ladbrokes bet wins. If the game ends 41-0, then the Bet365 bet wins and the Ladbrokes bet loses. Its down to the punters knowledge and skill whether they beat the bookie at rugby handicaps as there is effectively no margin in those bets if you use multiple bookies.
There are rare occasions where there are risk free bets or arbitrage. This is where bookies price too generously. The prices disappear pretty quick and the stakes are pretty limited. It is possible to get ahead using free bets and doing this but thats a completely different subject.
Bookies will ban winning accounts but will ban the accounts of arbitrages even quicker. They don't like them at all.