Betting exchanges enable sports fans to bet against each other on the outcome of a football match, horse race, cricket match and so on.
By eliminating the bookmaker's profit margin, they can provide a better value bet.
Betting exchanges are like eBay, they bring together people who seek better value by cutting out the high street.
Some betting professionals say you can tell the quality of a bettor by the quality of the records that a bettor keeps to assess progress.
To improve liquidity, Betfair uses cross-matching to advertise an unmatched bet to as many customers as possible.
The appeal of multiples is the huge potential return for a small stake and the excitement that builds whilst it remains a possibility for the bet to come off.