Don't worry Lin, my real name has three L's and two B's in it [it's French] and is often mistaken for my surname. Apart from that there are some very sharp female punters around !!

You are on the right track in my humble opinion in looking for 'value' rather than winners per se.

The scenario you describe is not to be worried about, because if you choose to only look at the 5 runners [where 80% of all winners come from] with the shortest pre/post odds [or the 5 best ratings], no horse like the one you describe would be among them as the runners shocking performance would be taken into account for you and reflected in it's pre/post odds which would also be shocking.