One of the hardest parts with the dogs is that the markets don't form properly until about 3 mins before the off. That's not to say you can't get things matched before but you certainly can't guarantee it. The problem there of course means you've got to be around to place the bets/lays or use some kind of auto betfair but that is painstaking to set up for 50 odd races per day! I've played around with various systems/tests etc and have consistently got pver SP + 20% on betfair on average with backing on the BAGS but it's very difficult to find something that works all the time.

With the lays I think you'd just have to set a cut off point and see how it goes. I would be surprised if any of your layed dogs that were 7 or 8/1 you could get layed under 10 on betfair unless you got something layed before market forms properly. Having said that there can be wild differences. I've had several taken at 8,9,10 on betfair and they've been 4/1 shots on SP. Not all winners of course but it shows the disparity in BF to SP.