Well, I've only linked to communities listed by the Tor Project itself.
Otherwise, the same way you would check whether HN or your local tea store is the NSA. You do your own research, run your own risk analysis, and if you want to stay sane, by default you give people the benefit of the doubt.
Generally, it's best not to run Tor relays from home as services will start to blacklist your IP as a proxy.
If you are going to be an exit node, then you should inform yourself about he legal challenges you might face, since you don't know what people will access with your IP address.
https://blog.torproject.org/tips-running-exit-node
https://www.eff.org/torchallenge/faq.html
Being an entry or middle-level node is less of a problem but some uncertainties remain, so this depends on your local laws.