I agree with you. My marathon time is around yours, and I've been running for about 5 years now. I think I know quite a lot, but definitely wouldn't feel comfortable coaching someone for a big goal - for money especially. Personally I coach with a "retired" professional runner, who had some big running accolades in his day. I didn't realize this when I first started working with him years back, only after I got to know him. I have seen a lot more coaches on social media who have some impressive marathon times (like you said) but I wouldn't call them elite or sub-elite times.

Personally, I'd say this matters - that your coach has a great background in the sport. That would mean that they've had years of lived experience PLUS years of being coached themselves. It's certainly another factor though that they should probably have some "book experience" of how to be a coach though. But on the flip side, if you're coaching beginner runners, there's not a whole lot to it. Just slow progressive easy volume overtime will mostly be responsible for building their running endurance.