Arbitraging is a way of betting that "locks in" a guaranteed profit regardless of the outcome.  It is a method often used by professional gamblers.  It is easy to do once you understand the principles.  Read on...............

Imagine a Baseball game New York v's Dallas.   You log onto a betting website and you see both teams are evens.  If you put $20 on each team then no matter who wins you will get $40 back and since you staked $40 ($20 on each team) you end up breaking even.  This is called an Arbitrage, but that is no use of course - why would you bother if you just break even all the time?

So you log onto the same website and it has NY at 11/10 and you log onto another website and find Dallas at evens then you have a "positive arb".   You can put $20 on each and if Dallas win you get $40 back (i.e. you break even again) but if NY win you get $42 back.   So no matter which team wins you can't lose!   You either win $2 or break even

Now you can go a bit further - using some simple maths you can calculate a bet amount to put on that guarantees a profit on the game.    In the example above you can put $20 on NY and $21 on Dallas.   If NY win you get $42 back, if Dallas win you get $42 back so regardless of the outcome of the match, you get a guaranteed profit of $1.

This is easy, but here is the problem - you have to hunt for Arbs - they are not easy to find.   The best time to find Arbs is shortly before game time or during the game itself, as the odds start to shift rapidly and Arbs will appear, but you have to be quick.   In-game betting is extremely risky if you don't react before the odds change.

Advanced Arbing
There are a few advanced techniques to help increase profits from Arbing -

Using Bonuses or Freebets - Most of the online sites give bonuses or Freebets.  If you deposited $1000 with VIP and got a $200 welcome bonus, you can "Arb" this bonus out by betting the whole $1200 on NY in the above game and then calculating an Arb amount to bet on Dallas at another site.   So for example, assume both teams are even money -

You bet $1200 at VIP on NY (your $1000 and the $200 bonus)
You bet $1200 at Linesmaker on Dallas

If Dallas win, then you have $2400 in your Linesmaker account and zero in your VIP account but you only bet $2200 of your own money!   You just made $200 profit and you didn't risk any of your own money.  If NY win then you have $2400 in your VIP account but $200 of that is the bonus money so you would have to do some more Arbs to try and get that over to Linesmaker or satisfy the rollover requirements.  Either way, you eventually end up with $200 profit.

Arbing Freebets is slightly more complicated if the stake in the Freebet is not returned.  email me if you want a calculator tool to work out the optimum way to Arb Freebets but in general use your Freebet to Arb on an outside chance (at least 3/1) and you will get about 70% of the Freebet value as guaranteed profit.

Finally - What if there are more than two outcomes?   There are two ways to deal with these:  either you do a 3-way arb (e.g for a soccer match which has 3 outcomes including the draw) which is more complicated and needs a calculator to work out the stakes, or you "Lay" your choice on a Betting Exchange like Betfair.   Laying means betting against an outcome so for soccer you could bet Chelsea at evens then go onto an Exchange and Lay Chelsea at evens.  That way the draw becomes irrelevant and it works like a simple 2-way arb.  Laying applies to all bets with multiple outcomes (like horse racing) and is a common technique of professional gamblers.