How to do it?

For example, you can bet the opposite results of the same sport event at different bookmachers. Let`s take as an example a fictional tennis match – Anna Kurnikowa vs Venus Williams. We can bet Kurnikowa`s win at one bookmacher`s and at the same time Williams`s win at the other one. If the rates difference is proper, we will earn some profit unconformably to the result of the match.

This is a similar situation to the arbitrage in the world of economics when i.e. we buy stock which have a bad quotation at one place and we sell it with a profit somewhere else.

Why aren`t there only millioners walking around if it is such a piece of cake?

Such profitable rates do not happen very often. Specialized internet services are engaged in analyzing and looking for those profitable rates. Then they usually sell that information to the potential "investors". Internet bookmachers offer the highest rates because the costs of running the buissnes are very low. Besides they are registered at "a tax free paradise" where they do not have to pay the tax (the player does not have to do it, either).

However, you need to have there quite a lot of accounts with enough money for playing. What is more, the players are emotionally engaged in the sport event they bet. Even subconsciously they want their team to win. And this kind of attitude may be very disappointing financially.

Well then no sentiments. We have to follow the hard rules of logic.

Absolutely. It is advisable to bet a draw of the teams. If we do not win, we need to raise the amount of money we play for, choose another match and bet a draw again etc. Until we win and the profits cover the costs of all the previous loses.

Of course it would be a good idea to look through the world league statistics (there are internet services offering that kind of information) and find one where the draws are statistically the most probable.