I have advocated finding groups in meetup.com and I have found some good ones, some that dissolved quickly, some that were boring or absurd, but I was shocked to find that you are on your own when you join a group. If you pay a fee and the leader wants to oust you right away, you are screwed. Meetup will not investigate it or the complaints about the character of the person running the group. You are on your own.
I have some tips to keep yourself safe if you're going to swim in that unprotected pool where anyone can run a group and do whatever they wish:
If the group is associated with a person's business, know that you will be bothered to perhaps join their yoga studio or purchase their DVD career guide package, or whatever else nonsense and you might be bothered a lot to do more business with their business. I shy away from any meetup associated with a business, spa, club, teaching group, or other organization that wants new customers. You are no longer a meetup member, you a client.
Be cautious of leaders who plan things and cancel often. They are flaky. If they constantly change location and date and guest speakers and cancel at the last minute, it's not worth playing tag with them.
Some leaders have a subtle agenda. They are looking for connections in a field, hoping to elicit free help for projects. If they want you to do work on a project together or something outside of meetup or give you business investment possibilities to consider getting in on, run--don't walk.
If you see members coming and going often and not staying, that's not a good sign. Either the group is disorganized or there are issues on the side that you don't know about. Some leaders use groups as a way to meet people to date, or people to befriend and then personal tiffs get in the way and members leave.
Take the necessary precautions to keep it only a meetup. That means, do not invest in their deals, give them a bunch of cash and if they have a fee pay by PayPal so you can dispute it, do not do things outside of meetup with them or help them with their own moneymaking schemes.