I wasn't coached online, only in person. I also coached myself for years.
But I am coaching online for free, at least until I'll have a portfolio.
I also assisted coaching in person.
I can tell you the pros and cons of having an online coach.
If it is a coach with many runners, he may pay less attention to everyone.
An online coach cannot see you running and your habits. So you are on your own on many aspects.
I would say that someone is experienced in running after watching, tracking and meeting in person over 200 runners, in the course of ~5 years.
If you didn't, then this would be a good reference point when choosing an online coach.