I outlined the method in the first post. I don't want to give exact rules but I have given away more then enough information for anyone wanting to follow what I do (if they do a bit of their own research). All you need to do is analyse the prices of various sources to come up with an expected chance for each horse. You then add a risk percentage and determine if the price available on betfair is a lay or bet.

The way you come up with your concensus chance estimate is the only thing I didn't spell out. I record the results here for myself mostly, but it can also be used by others to see if they want to research their own methods on determining a consensus chance.