hang on i think the light bulb just turned on, after having a play with the betfair system.

I see its not like tab where i can't set the odds. Betfair lets me set what I want for say a win bet (I'm the backer ie betting like at tab). So for example for a back bet I can set the odds to whatever say the favourite on the tab is showing 1.50. I could put up $4.30 but this won't get matched by any layers out there. So this would explain by the two columns differ. Whereas the lay column I'm saying, hey punters I'll give you say 200-1 if you bet 5 units if this horse wins if not I get to keep your 5 units. So as a layer I wouldn't put up short priced lay odds even tho its a high possibility it won't win, as I have to make it worthwhile to the punter to give me his 5 units?

Correct?

Person making a "back" bet sets the lay price
Person making a "lay" bet sets the back price

So all betfair is doing is when there is a match of two sides of that bet we have a bet?

You: I want to bet 10 on No 8 to win at odds of 3.40
Me: I want 10 on No 8 to lose, I'm willing to give odds of 3.40 to anyone out there willing to bet 10 units at my odds.

Sorry I'm a bit daft but I get there eventually.