Generally speaking
If one is looking at a failed win only system as a possible laying system , the loss result has to be a min of -30% LOT if using TAB prices to work out past results.

The reason being that one has to assume Betfair prices being 20% greater than TAB prices.
Thus leaving us approx 10% POT.

So when we get bit , we will be trying to recover this & some.

If any one wishes to have a crack at Lay betting ...here's a tip.

Try & target only one selection per venue.e.g. 7 venues = 7 selections.
Bet .6% of bank.
Lay Price 3.50 $9.80
If all are successful = 4.2% increase on bank.

You will find that ones success rate will be a lot higher doing it this way,
Try it for 7 days & look at your results. You may be surprised how good you can be ,doing it this way.

But don't try & kid yourself that you can do it 5 times per venue at all venues, all the time, I wont happen.

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Cheers.