My sources are a mix of
AIUK discussions, friends/clubmates and self-taught.
Coaches? I've heard of them. Not sure what they look like, though I've seen more than my fair share of club members who think they
ought to be made qualified coaches, but without having to do any of the pesky qualifications.
Actually, I've had a real coach appraise me for 5 minutes once, which then saw me break 500 indoors for the first time.