Benny, what I did was basically use the Pre-post market AS ratings which they are (in a way). Just by taking the pre-post fav you will place around 60% of the time and make a loss of about 9% on T/O. By taking the first 3 in the pre-post market you will COLLECT around 85% of the time, sometimes with one placing, sometimes with 2 (fairly often) and occasioanlly with 3. Personally I would not go any further than this because as Lin says there are 3 place divies so you can potentially collect on all 3. In terms of level stakes you will probably lose about 12-14% on T/O, though if you always invest at best tote odds (Sporstbet) this figure will probably improve.
By applying commonsense filters either to the types of races/days of the week etc, and/or filters to the selections themselves you will again improve this situation, personally I never got better than break even (over time).

Now, when I applied the same filters to Top Rated Horses from a "well known" ratings service, I turned a profit and have been doing so for over 2 years. I guess the difference here is the quality of the "ratings".