There is no such thing in the world you may say but there is. A sure bet or a risk free bet is a bet, where you will win no matter the outcome. How does this happen? A sure bet appears when bookmakers have different estimations about the outcome of an event. You won`t find a sure bet within a single bookie since they operate on a following principle:

Payout =

1
------------------------------------------------------- = < 1 (100%)
1 / home odds + 1 / draw odds + 1 / away odds

The payout percentage differs among the bookies but is in general between 80% and 95%. But if you search for best odds for an individual outcome among several bookmakers then we might find a sure bet or a payout > 1 (100%).

Example: England to win vs. Germany

Home odds: @2,50
Draw odds: @3,50
Away odds: @3,40

Payout =

1
---------------------------------- = 1,0206 > 1
1 / 2,50 + 1 / 3,50 + 1 /3,40

As you can see from the formula you will have a guaranteed profit of 2,06% no matter the outcome of an event if you would have covered each outcome. This means that for every 100€ staked you would got back 102,60€ - regardless the outcome. You need to calculate the stake ratio:

40,82 € on the home win (How to calculate this? Just divide 102,60 by odd : 102,06 € / @2,50 = 40,82 €)
29,16 € on the draw (102,06 € / @3,50)
30,02 € on the away win (102,06 € / @3,40)

It is evident that you would be in profit no matter how the game ends. You have staked (40,82 + 29,16 + 30,02 = 100 €) and the payout was 102,60€ thus securing a profit of 2,06%. Your guaranteed profit with sure bets is usually between 0,1% and 15% and rarely even higher.

Sounds great? It is but before you resign your job :) you should consider following: you must have several accounts with many bookies to take advantage over best odds. Not every bookmaker is reliable and some operate with low betting limits. Because guaranteed profit is small you must deposit and bet higher amounts and this can result in various expenses that may take away your edge.

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Source : Sure Bets