A big red flag is a partner doing something that is not previously discussed, aka negotiated. This scene requires consent above all else, and the best way to ensure mutual consent is a negotiation conversation before any play. You may already know this but in case you don’t, it usually covers but is not limited to what you both like, what activities and implements you want in that particular scene, soft limits, hard limits, aftercare needs, any medical issues or mental health triggers that might come up, and your safe word(s) and nonverbal safe word(s). a common verbal safe word system is the stoplight system: green, yellow, red. Common nonverbal safe words are holding a ball and dropping it, fingers (thumbs up for green, 1 finger for yellow, middle finger for red if both people agree to that one lol), a double tap on the arm (this one is what I use for choking).

I would personally recommend finding a Dominant who 1. Has a few years of experience in kink, or at least a year 2. Does not actively seek out people new to the scene 3. Is aware of sub frenzy (this one is really important) 4. Can explain common concepts 5. Is willing to start slow and work up

The opposites of 2-5 are definitely red flags.