[jfc]

A few things:

1) People's words are like deep water. Pay careful attention to what people say--it's profoundly revealing (more than they realize). By listening, I've been able to identify people who intended to trouble me in some way. It's incredible, they just can't keep it inside even when pretending to be nice.

2) Actions speak louder than words (given #1, this is really saying something). Don't look for people to be who you want them to be; wait long enough for them to show themselves. And they will. ETA: You may occasionally encounter someone who is able to fool you for extended periods of time, like years. But even then they often leave useful clues as to their agenda.

3) If the product is free, the product is me!

[sufiyan]

Could you expound on (1). I have been toyed around by my former Co founder who sweet talked me into believing him. I still think I suck at understanding human behaviour and nature. Are there any telling signs that help you?

[cannabisceo]

Most often I've seen it in the form of jokes. You're in the final stretches of negotiating a deal with someone you consider a friend and they make some joke about how now they're going to stop showing up to work. Red flag. You might think "why would someone say something like that?" I was negotiating a deal where the other party was guaranteed 7.5MM over the next 5 years. They made the joke because they thought they already had me wrapped up in the deal. I walked away based on that joke alone. The logic is that at some level they're trying to prepare you for what you're in for. Everyone's armor has chinks. As the deal gets closer to being done you see the real person on the other side of the table.

Another red flag is if you put something in email and they call you to respond on the phone. I treat email almost entirely defensively now. It's simply a record of things I'm comfortable being read aloud in court and a memorialization of what was agreed to in conversation. If I'm not comfortable with it being read in court it's discussed on the phone or in person.

[jfc]

First, an example:

Decades ago, a friend of mine at the time (female) met a guy. She was really beautiful and a genuinely nice person, so lots of guys would ask her out. She told me about a date with this one guy, and he didn't call her again. Even though she hid some of the details, I was able to ascertain the general contours of what happened and was able to figure out his agenda. How? Because of something he said to her.

She told me that he picked her up and they went out for diner, but when he dropped her off at home he became concerned about parking, wondering if a garbage truck might pin him in the next morning. At the time, she thought nothing of that. But she explained to me that she hadn't planned for him to stay overnight.

But what he said was a pretty BIG siren. It was obvious he already intended to stay the night, otherwise why would parking the next morning matter? My guess is that if she had known his agenda she would have viewed him differently and maybe been more wary.

End of story? He never called her again. She was mystified as to why. I thought: well of course he didn't call--got what he wanted!

In response to your question, wouldn't say that there are telling signs, it's more about the content of what people say as the story above illustrates.

A few other loose thoughts about understanding people:

1) It's dangerous to assume that other people think as you do. In fact, people come from a range of contexts and backgrounds which are not obvious when you meet them. They are perfectly happy to smile and nod with you while completely disagreeing.

2) People are heavily self-interested. Unless it's your mother (and sometimes even then), expect people to look out for themselves first. Someone making a show of sacrificing for you? Hmm.

3) People enjoy feeling superior to others, even in very minor things. Shrewd people know this and use that information to their advantage. (Not advising this, just saying what people do).

4) Chinese proverb: the dog that can bite doesn't bark. When people have the capability to get you, they don't have to talk about it--they do it. The big talkers generally don't have the ability (though there is the occasional outlier).

You may want to look into some books on this topic. A useful one is 48 Laws of Power by Robert Greene. Not saying that you should follow his advice, but it is useful in understanding games that people play at work.

Book link (not affiliate) - https://amzn.to/2dzBqXD

[itronitron]

Telling signs include how they react to people that aren't telling them what they want to hear, this could be a supervisor, waiter, colleague, IT support, etc. You may need to adjust for local culture (i.e. Boston vs. SV),

[stevenkovar]

Input vs. Output. Does the person talk about how they're going to act more than they actually act? One of the biggest tells for me.

[ItsMe000001]

I'm not sure direct advise such as what you find in books, articles or some courses actually helps all that much - not by itself. I think such advise targets the wrong parts of the brain, the ones for conscious thinking.

However, I think by far the most of "people understanding" happens in the not consciously accessible parts. So I think that the best way simply is... experience and time. What really helps is if you actually want to understand other people, if you are curious. If it's like "work", like studying for an exam, something you were told is necessary but deep inside you'd rather do something else, your (unconscious) brain won't cooperate.

There's a lot of circuitry taking input from the visual and also from the auditory areas of the brain that do a lot of subconscious processing, and they "train themselves". Book knowledge is of little help, it can aid indirectly at most. The good news is, pretty much every one of us already has quite high abilities in this area, the main problem may actually be that you suppress what your deeper brain is trying to tell you. You probably already have those magical people-understanding abilities in a pretty advanced form!

Deep inside I knew perfectly well I was being screwed over during my first trip to the US in one of those New York electronics stores - but I suppressed it and spent a huge amount (for a poor Ex-East German student) on electronics I didn't need and that were 500% overpriced :) Just make sure that your losses are small, like mine (I think I gained a lot more during that simple encounter than I lost), don't try to avoid it or fret over it when you make such kinds of mistakes due to not understanding other people (or suppressing it without realizing it). Imagine that you just paid tuition for the best university there is to understand other humans.

Another issue related to and responsible for suppressing those instincts is that actually acting on them often is more work (at the immediate point in time) than just going with the flow (and suffering later). Example in your case, but same with any relationship: You actually know it's over, and much later, in retrospect, you will know that you already knew, but actually taking the step and ending it right now is really hard. But here again no external advice to your conscious self can be of much help. Especially since only you have all the information about the specific information, so asking others who don't have all that context for advise seems to me to be a form of procrastination - you did something (ask others) so that feels good, but it should be you yourself who makes that decision since only you know what's going on and the people involved.