Neurodivergence

I feel like listening to your gut is a big component of this. There have been times when I notice that the way someone talks bothers me for a reason I can't put my finger on and I decide to give them the benefit of the doubt, assuming I'm being shallow or unreasonable, but then a few months or even years later their behavior lines up with my initial discomfort and I realize I had spotted something being off from the start. Sometimes it's better to listen to the general feeling you're getting from the less verbal and analytical parts of yourself than to wait until you have a real explanation.

Of course, there may be people who are just anxious or a little eccentric and that's what you're spotting, but usually it's worth at least sniffing it out from a distance rather than fully ignoring those feelings until you can articulate the reason for them.

Could you be a little bit more specific? Do you have an example or two of people/situations you struggled to navigate? Bad intentions can mean a lot of things and understanding how you respond and how you wish you were responding could both be really helpful to figuring out where the process is breaking down and what skills might be most useful.

I personally always had a tough time with spotting bad intentions, and I started to always tell people

"let me think about it and get back to you"

That lets me get the distance and time to really assess the ask: does it help me, does it hurt me, does it hurt someone else, what does the asker gain from it, why would they want that, etc.

Generally, if someone is pressuring me not to take time to give an answer, I take that as a red flag. And for me at least it was tough to learn to ask for that time, but it's such a huge help in avoiding people with bad intentions.

Boundaries.

Why do predators seem to always find the person who will let them sink their teeth in? They're not seeking intelligently. What they're doing is pushing boundaries with everyone. People with healthy boundaries are pushed away, people lacking boundaries let the predators in. The reason the predator got to you was that you either set no boundaries with them or you folded on a boundary you did give showing them how they can further take advantage of you. I was raised in such a way as to tolerate abuse and neglect so my boundaries let the predators right in historically.

"Predator" might seem like a strong word for emotional vampires, closet narcissists, and dependent personalities, but what they are doing is victim seeking. They can't be another way until they identify their own behavior and choose to be another way. Let them push you away when they push your boundaries.

There are some great suggestions here! It feels like a lot to focus on each of these things when you're not practiced with these habits being suggested, but gaining proficiency in any of them will help to improve the others.

This link (PDF) is one of the Toastmasters resources on body language. Some of the tools presented there will help you to more effectively nope out of situations when you become uncomfortable, and hopefully empower you to feel more confident making those calls before it becomes too costly. I think it will also assist you in catching these occurrences earlier, since incongruities between what's being spoken and what the other person's body is saying can signify that there is a disconnect in intentions

i think this one starts with you

one half of the equation is to be comfortable and firm in your boundaries. if someone asks something of you that you're not comfortable with, don't do it. say you're not comfortable. if they insist, or say it's normal, decline again and leave the interaction

this is the bread and butter of navigating these encounters. if you're not comfortable with this, try to practice with a mirror, a trusted friend, or a therapist

the other half of the equation is to get in touch with your own feelings and emotions. the best way we understand others is by understanding ourselves. take some time to practice mindfulness meditation and spend that time listening to and observing how you feel. as you practice more, this skill will come more naturally to you in day to day interactions. soon, you'll be able to tell when people are being fake or manipulative by understanding how you feel in relation to it

you may think this won't help you understand others, but humans are wired with very good mirror neurons which are very perceptive of how others are feeling. when you understand how something feels for you, you will understand how it feels for someone else, and you'll be able to notice more subtle things like a missing emotion - for example, a lack of joy when feigning interest in something you're interested in

both of these take some time and dedication to develop, but i think it will help you with your problem

an additional skill you will probably want to pick up is breathing practice. check out 4-7-8 breathing (the first number is the count for inhaling, the second is for holding, the third is for exhaling; so breathe for 4, hold for 7, exhale for 8; if this is too hard, you can try 4-4-4). this is to help keep you calm when asserting boundaries or remaining patient with your feelings during meditation

*_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).

Improve your empathy. It sounds hard, but when you focus on body language it gets a lot easier. People will give away what their goal is before they even spit a word. You can say "Hey" to them and that is most of the time all you need.