I estimate that 80% of the driving horses I've had in to re-school have nothing wrong with them at all other than they're harnessed or put to incorrectly and so basically I just adjust everything so its right and put them to in the proper position using correct adjustments to a carriage that fits them and they NEVER EVER do anything wrong.
I also have gotten much more cynical about folks and their horse experiences, knowledge depths. There really are not that many who go beyond book work, put in enough time to learn enough anymore. No depth to them. Or they are learning from their mistakes, a bad method, yet don't want to change.
To end this posting on a lighter note....
My daughter is much the most closely observed, frequently corrected child, in her horse group activities, horse handling at home.