The reason we generally get a coach is because we don’t know enough to help our kid enough on our own. That also means we don’t know enough to know if the coach doesn’t know what they are talking about.
This isn't, or shouldn't be, true.
Long before I developed the ability to teach the basics of pitching (and I still don't want to go beyond that), I learned the good/bad. I learned what to look for in a pitching coach for my players.
It's possible to learn enough to recognize good instruction without knowing enough to teach it all yourself.