Its all getting a bit complicated. If you have a maximum liability (like $33) THAT IS ALL YOU will pay out of your account regardless of the money taken in from the other party.

$34 horse - If the horse wins you pay out your liability of $33 and give the guy his $1 back.

$2 Horse - If you've decided to have a maximum liability of $33 on a horse at this price and it wins you pay out your liability of $33 but also have to give back the back bet that the other party would of placed which, in this case, happens to also be $33 making it $66 going into the other guys account ($33 of your money and his bet returned).

$10 Horse wins with a liability of $30. The backer would of had to place a $3.33 bet to win $30. You therefore have to pay him $30 from your account and his $3.33 back as well. If the horse loses you keep his $3.33 (less commission of course).

I hope this helps (and I hope its right).

__________________
Never give up on a dream just because of the time it will take to accomplish it. The time will pass anyway.”

― Earl Nightingale