Ziay!

Peter Cooper

If the odds with different betties are different, couldn't you pick the best odds for each way and put bets on every outcome with different bet-takers to get an overall win?

Andrew Norris

If you can get odds that sum up to be better than even, yes.

This doesn't usually work with professional bookmakers such as Vegas or online casinos, because of two reasons. First, they take their cut of the bet out of the odds (that's how they make their money), which means you need a substantial differential to gain an advantage. Second, the odds at the various casinos usually track each other pretty closely. If one casino is offering better odds on one side of a bet than the others, people betting that side will tend to bet at that casino disproportionately until it evens back out again.

However, if you are betting with individuals and you are setting odds with them, there's no reason you can't bet with different people to get better odds, as long as you can convince them to bet with you.

In fact, even if you don't bet on both sides of an event, if you consistently get better odds than average, you will tend to make money over time.