I,m not up with this new fangled Betfair stuff.

Yep another example, classic case of being awake

I can't quite see how you win here.
Could you please post your exact wagers on this race so I can understand how it works?

Not sure how much the bookies will take but lets just say you could back it for $200
Back $200x$31=profit $6000
Lay $344.44x$18=liability $5855



Win or lose you collect about $144 a bit less on the loss because of commission.

The calculation to work it out is Stake x backprice/layprice

So if it wins I collect $6000 take away $5855 what I lost on Betfair.

And if it Loses , how much do I get back from Betfair?

Ah okay
I see it now

I get back $344 minus 5% means about $330 .
And take away the $200 on the Bookies leaves $130 Profit.

Be funny if after backing it at $31 and going to Betfair to lay it , the Punters decided they dont want to back it any more.

$327.21 after commission less the $200 for the back bet so $127.21

This is the same formula used when trading but if you were laying first it would be
lay stake x layodds/backodds

This gives you equal profit win or lose minus commission.

Cheers Shaun, you're pretty much spot on.

Had $200 @ 31, and laid $363 @ 17.12.

Wins = +$6000 - (363 x 16.12) = +$148.44
Loses = -$200 + (363 x 95.45%) = +$146.48

I'm on 4.6% commission.

All I look for are runners that are 95% or less of the bookies price, and that there's plenty of liquidity. Yesterday there were none but today I got on 10 which is very unusual, and just missed a few others.

How many bookie sites do you look at?