I'm really not qualified in any way to state the below, just trying to draw from my personal experience and express what I think is useful and relevant in this situation.

English is not my first language

Honestly I think it is more useful and helpful to focus on the second part of the equation: exiting the situation.

Exiting situations is a tremendously useful life skill regardless of the other person(s) intentions while spotting people with bad intentions could become a burden as it might lead you down a path of mistrusting many more persons than you "need" to mistrust.

Learning to say "no" in different and effective ways is also a way to learn to say yes and will, in my experience, let you live a life closer to what you want.

I suspect that I'm still early on my path to communicate this effectively because I was not really listened to as a child, so my feelings and wishes where not seen as relevant to a situation.

As for how to do it: I don't really have anything groundbreaking to give you. But as with most things I suspect it's just practice: start saying no! And start acknowledging how you feel or felt even if it's too late to do anything about it as that can teach yourself to look for clues (inside yourself) in the future (maybe).