Odds.Plumnet.dk explains how to maximize your profit using sport bonus arbitrage.

Many bookmakers award new users a 100% bonus on their first deposits. If you deposit 50 € the bookmaker gives you a 50 € bonus.

The catch from the bookmakers is that they require that you wager your money a number of times, before you can withdraw the money.  This can be circumvented, by betting on all outcomes of a game. This way you can satisfy the wagering requirements, and keep your money, no mather the outcome of the game.

For this reason bookmakers will not allow you to bet at multiple outcomes of the same game, but by opening several bookmaker accounts (each with a bonus), you can bet at one outcome at each. So you can satisfy the wagering requirements, without taking any risk or breaking any rules. 

This site explains in detail how this can be accomplished, lists bookmaker bonuses, has a form to calculate the optimal wagers and has sections about other related stuff.

Read more here!
 

The site owner has no affiliation with any bookmakers. I have used this idea to earn some extra money during my studies. This worked very well and since it can be done by anyone with a credit card and some time at hand, I have made this site about it. The site is non-profit, made for my own amusement.