Shaun is right on the money!

Unless you can say with 100% confidence your $2.00 rated horse will win 50% of the races long-term you can't predict an underlay or overs.

Something interesting and sorry a little off topic, is if the prizemoney pool like on a Saturday is around $1Million on a particular race. This normally is contributed by many thousand punters. Basically the starting price is very close to its true value.

But if you can use a ratings appraoch and find value in the old country races or mid-week maidens with a smaller pool and maybe a specific angle you have that may not of be considered by others, good luck to you. A little more challenging but where there is some value.