Quote from Chrome: "A good reliable ratings service will not boast "we picked more winners than the public". It will find value bets or overlays and identify where the public have over-bet (confidence, hype etc) or underlay".

...and just how does a rating service recognize and supply 'overlays' to subscribers when that info cannot be known except minutes before a race?

I used to get my ratings Sat. morning and whether the public is going to back the selections into underlay or overlay [if the rating service also supplies a price for a selection which they usually don't] is unknown to anybody at that time. No rating service or anyone knows what price a horse is going to jump at.