In the UK and in Australia, Betfair operates a betting exchange which is a bookie using technology to make sure you get a better price. It does that by eliminating its risk, which means it doesn't have to build in extra margin as a safety cushion. The effect is that Betfair punters bet on the price they want, and not the price they're told they can have.
For example, imagine two friends having a bet while watching a football match; an impartial observer holding the money while the game is played. A betting exchange works in the same way: our punters bet against each other, and Betfair hold the stakes until the bet is settled.
By contrast, in Malta, Betfair is a bookmaker which allows non-UK registered customers to bet against Betfair, but still at prices set by other punters.