This is pretty general in scope and not related at all to mechanics but I believe more head coaches should operate this way....at least until they're coaching an Olympic team.
https://www.flosoftball.com/articles/6330159-how-to-pick-the-right-softball-pitching-coach
https://www.flosoftball.com/articles/6330159-how-to-pick-the-right-softball-pitching-coach