Ok, thanks vertical
So you actually bet the liability amount when booking on Betfair, not the stake amount?
Think it's starting to make sense now. When you place a lay bet, you're not 'hiding' anything from the exchange... they know you're doing it to offset a back bet. You enter a particular stake (in my case £15), because the exchange odds are different to the bookies odds, so you're basically working out the equivalent bet?
But actually, in the same way that the winnings at the bookies aren't the same as the stakes, the potential losses (liability??) at the exchange isn't the same as the stake? It's just, I have to pay the potential loses (liability) upfront?
But, I'll either get it back if the exchange bet wins, or the bookie bet will cover it and then some?
Is that right?
Presumably then, people don't get gubbed for the match betting bit, per se, they get gubbed for only ever taking advantage of offers and not losing any real money?