He covers it so much better than I would although I do want to add a few things to this. For a start, a perusal of :
The Advanced Bonewits' Cult Danger Evaluation Frame and see how it fits with the group that you're looking at. It can be scary how many facebook groups tick too many of these boxes, never mind offline groups that meet in person.
I'd also look at how questions are treated.
I ask a lot of questions. Sometimes it's because I don't understand how you managed to come to that conclusion and I'm trying to figure out the whys and wherefores. Sometimes it's to see if we're using the same word but have different meanings. Sometimes it's because I've never heard of what it is you're talking about and I'm always keen for a learning experience. And sometimes because by making you think about the questions I'm asking, I'm hoping you'll figure some things out for yourself.
The responses I get can be very telling of whether you're someone worth listening to, someone to just ignore or someone to run from. And I'm not just talking about the content of the response. I'm talking about the way in which the response comes.
Does the response seem angry? (As in "how dare you" rather than projected emotion). Does it seem to make them nervous? Does it get ignored or brushed off? Do you suddenly have a lot of others jumping in to tell you off for asking? Does it get treated as 'negativity' or 'being a smart arse'? Do you find your question has been deleted? Do you get a lot of waffly ramblings that skate around it but don't actually answer your question?
I treat all of these as warning signs. Sometimes it's warning you that they don't really know what they claim to know but won't admit it and sometimes it's a warning that you're dealing with a megalomaniac who's trying to control everyone. Sometimes it's a warning that there are mental health issues going on.
A worthwhile teacher or leader doesn't mind being questioned. As long as it's done with respect and not as a demand or expectation.
Another one that Morgan touches on but I wish to expand further is the following:
5. Does not cite sources – magical and spiritual knowledge does not grow in a vacuum. A leader or teacher who never mentions who taught them or the books that they have read is guilty of trying to conceal their past. If they try to conceal their past, then what else are they hiding? Especially troublesome are those who claim that all their knowledge comes from Secret Chiefs that only they are spiritually and magically advanced enough to meet.
Morgan is speaking more of Ceremonial Lodges than the average pagan or witchcraft group, but this does carry over. The point I wish to highlight in this is the last part - all their knowledge comes from Secret Chiefs that only they are spiritually and magically advanced enough to meet. I've met self-appointed leaders who get all their information from "their guides" or "the Gods" or some special spirit they've channelled. Unless there is some way to verify the information, be very very careful.
A prime example of this type of thing is the Ramtha Cult.
One I've experienced claimed she had a channelled message from "the Goddess" for everyone at our ritual. I've never found the Gods shy about making their wishes known to me, they've never used the flowery "dear one" type language when talking to me and the instructions (and yes they were instructions) fit neatly in with what the channeller had been pushing for, but were completely against the direction my Gods had been pushing me. I left that ritual angry at her for her attempted manipulation of everyone present and for believing that we would be gullible enough to fall for it.
I'm sure there's more I've missed, I'm sure there's stuff that's become other people's personal red flags. These are just the main ones that I've experienced.