errrr...no!

Go back to the example>> if you did offer the $20 odds and let someone on for $10 you need to have the $200 in your account to cover it.
When you hit the bet button to finalise it all it will automatically deduct the $200 from your account << even though the race hasnt run yet.
Think of betfair as your mates girlfriend >> who holds the money << whilst the bet you have with your mate on who can eat 5 hotdogs the fastest is finished.
They are the mediators who hold the money.
You have to put the money up front and out of your account until the race is over, If you win and the horse loses you will get back the $200 + $10 of the punters losing bet back into your account.
You cant offer odds and bet unless you have the money that you can give to betdfair to hold until the race is over.
THis stops you from making lays all over the place with a bank balance of $0. If you lose those bets and all those horses win how would they get the $$$ of you? >>> you have to have it in the first place then pass onto betfair as the holders / mediators when applying each bet.