I have been playing round with the idea of laying at the moment. At present the idea is showing a 25% LOT using betfair prices after 5% deductions. Now, this method has come from filtering a win method so have not been recording lay prices, only have the available win prices which I could have taken. I notice that generally the available lay prices are slightly higher than the back prices, is there a general rule as to what I should add to check if the method is actually viable laying? So showing a 25% LOT, would adding 5-10% to that be realistic to give an idea of what laying would show?