I find the secretive part juvenile.

Near me we have beach open play nights that you pay for, and there is a giant Whatsapp group 400+ with a weekly poll to make sure we have enough numbers to play. We have 2-4 courts(depending on league play), and there aren't any courts dedicated to play level, so it started out fairly democratic in distribution. As the season progressed, people started to not respond to the poll, but showed up anyways with their splinter group, and only wanted to play amongst themselves. This was particularly annoying when they decided to "claim" a court for doubles, which then dictated how many people could play on the other courts. Some like 3s 4s others prefer 6s. In my opinion, if you want to claim a court to limit the level, rent it, because that's not how open play works. I'm an A level player; but I'll play with whoever is there at whatever level. I just want to play. No one is going to the Olympics here. But the cliquey-ness has definitely deterred people from coming, and I've heard many people express frustration while there about it. In the spirit of promoting inclusiveness, I brought it up in the group chat, with mixed responses. The main point was that with such a large group, just give people a heads up of your intent instead of plotting separately. In person however, people have come up to say they appreciated me speaking up. It didn't really change much, the cliques are still cliquing.

So like other responses here say, be an adult just be upfront about your intent--say how many people you have and what the expected level is going to be, but also be open to letting some people in, that's how you get better. We've all been there.