Friend of mine uses this angle heavily and hits some gigantic long shots. This angle happens when the horse has a better jockey on it than it should have. Here is the race snap-shot that inspired this blog. Not a long-shot but the #2 has a 0 trainer and a 7 jockey at 4-1. Gets A+ grade and wins.
There are multiple examples you can find
1) In my RISKY HORSES blog I wrote the following... "Horse has a very poor trainer (6+ points lower than the best in race) with at best an average jockey." Now the opposite could also be true. A very poor trainer could have a superb jockey on it (6 points better than the trainer). Good jockeys don't ride for bad trainers unless the horse is good. Where you draw the line on jockey and trainer score is important. But if the delta is very large take a hard look.
2) A good jockey is riding for a long shot. Now the jockey may always ride for a trainer who has a bad horse in this race but typically good jockeys and trainers want to win races. So look for really good jockeys on horses at 8-1 morning line or better.
3) This is tied in with #2 above but if a horse gets a "1" in the last spot in the RANK column then the horse has the best combination of jockey & trainer. See my RANK blog. This horse will get at least a C letter grade as well.