The liability is a minimum of $30 however that does not apply if you want to lay something that is paying under $30 liability for the minimum bet of $5.

So if your laying the fave that's paying $3.00 and lay the horse for $5 (the amount you will win if the horse loses) your liability for that race will be $10. That's worked out by multiplying (the price of the horse minus 1) by the stake amount.

So ($3-$1) = $2 Horse x $5 stake = $10 liability.
Or ($5-$1) = $4 Horse x $5 stake = $20 liability.

You can also play around with the liability amount on the betfair web site until the liability equals how much you want before you submit the bet.

I hope that makes sense.

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

― Earl Nightingale