You probably didn't mean it that way, but comparing non pros with "black market" may be misunderstood.
I conduct most of my sessions with a non-pro and friends of her. She has been introduced to me by a pro (with whom I also regularly play).
I also like to emphasize that the "cheaper" doesn't apply to my non-pro sessions, they turn out to be more expensive.

But I do find your editorial guidelines interesting from another point of view:
Historically, guilds have had a purpose of establishing quality standards. However they mainly served protectionism. Eventually, they crumbled because they couldn't keep up with innovation.

Is it possible that this site is following the same fate?
Another popular thread is titled "Where have all the topics gone".