Only time I ever put money on at the bookmakers, it was because I knew I could beat the odds: I had a 100% chance of winning.
A few years ago one of the Online gambling sites had a promotion to encourage new Users: For every £1 you placed on your first bet, they would match it up to £100.
I put in £100 and got them to match it. Then I split the £200 on a football match- half the money that side A wins, half that they don't.
Inevitably, I lost one of the bets and won the other. I think I wound up with around £120, so I simply withdrew the cash and closed the account.
This little loophole in their promotion had been publicised by
www.ntk.net (that's how I came to know about it) and I wasn't the only one to pull it off. The offer was soon withdrawn...