I plan to do this on Saturday Metrop meetings for a while. It shows a much better result than Country or Provincial. Still, I thought I would do todays meetings, just to see what difficulties there are in deriving selections.
Rules:
Candidate races (inlcluding Maidens, but not jumps, all field sizes) have a single top rater, which does NOT meet Michaelg's criterion of 'last two placed-positions to be between 3 and 6 points, and unbroken by a spell'.
Top rater must be below $5.50, but above $2.00. (If outside this range, again not a candidate race.)
Back the two lowest priced horses other than the top rater.
Actual prices (one minute to go?) are best, but I'll try with AAP prices. This presents some problems when get multiple equal prices - can result in single selections when cannot identify a clear second selection. Also, with scratchings, need to re-calculate market to check if, for example, a top rater at $6.50 may fall below $5.50 with scratchings.

Today's selections are:
Queanbeyan: R1 numbers 3 and 6, R2 3 and 9, R3 4 and 14, Race 4 1 and 2.
Muswellbrook:R2 1 and 3, R3 2 and 5, R4 1 and 10, R9 1 and 5.
Moe:R1 8 and 9, R2 1 and 6, R5 3, R6 2.