Here are some resources I've come across for safety in hypnosis, especially for subjects. You are playing with your mind, and that needs to be protected.
Structure of a session
I'd say it's good to stick to something like this, especially if you're a first timer or trancing with someone new. If the hypnotist doesn't already follow this structure, it's a good idea to guide it into one like this.
Safety suggestions
It is a good idea to throw at least one of these in every session, if not every few sessions. Some good tips at the bottom for red flags and keeping safe, too. Request for these if the hypnotist does not mention that they will use these, especially if you are new.
Professor X Allie
Being risk-aware
There's a whole list of risks here, and the last section on abuse is a really great one for things to watch out for.
Community blacklist
I'm not sure how active this blog is, but it'd still help to keep an eye out for these people, since some of them are still active.
safehypnosisBambi Sleep and Tulpa
These are banned topics on a server, and with reason. Please do your own research before listening to the files - they could go awry. You should be wary of anything involving personality creation or replacement, especially permanently.
Name and shame
Not really a proper resource, but please report to moderators (if it's on Discord) and reach out if you need help.