Christian Osgood says the best way to judge a mentor or course is to look for an active community around it. Check for raving fans, regular interaction in online groups or meetups, and visible growth. A thriving community signals the mentor is passionate and the material actually works.
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It could be online, it could be meetups, but is there an actual community built around this? I found that if it's a really lame course or there's no support for it, people get the information, even if it's good content, they get the information, they go do something else, they join a different group. Are there people who are raving fans of this thing, whatever it is, who stick around, who are interacting with each other? If there's community around it that you can plug into, could be a Facebook page, could be a meetup, is there thriving active community where you can connect with community members and, and you can see the growth. If you have all of these things, it's very likely a great course taught by a great person who's actually passionate about teaching.