Studies show if someone seems extroverted, confident , religious or conscientious - they probably are. And if they're good-looking, trust your instincts even more. Why?

We all pay more attention to pretty people - and so our evaluations end up being more accurate :

Overall, people do judge a book by its cover, but a beautiful cover prompts a closer reading, leading more physically attractive people to be seen both more positively and more accurately.

And Sam says you can trust someone's visual "identity claims." These are the things someone chooses to display that says something about who they are or how they want to be perceived.

And there's one other thing to listen for while they're yakking. The word "I" can be very telling...

Powerful people don't say it much . Less powerful people say it the most:

Pennebaker finds that people who use "I" at higher rates tend to come across as more personal, warm and honest. While people who use "I" at lower rates come across as more self-confident... He also finds that the highest status person in a relationship tends to use "I" the least, and the person who is the lowest status tends to use the word "I" the most.

A class ring. T-shirts with slogans. Tattoos. Pay attention to them because they're usually accurate signs. Here's Sam :

Now this is all pretty personal. So what about if you're trying to read someone in a professional context?

Want to know if someone is good at their job? Then watch them do it for thirty seconds - or even just six seconds . Your guess about their competence is more likely to be right than wrong:

Want to know if someone's smart? Research says this is hard to tell from mere appearance when evaluating adults. But there's a trick that can help. Are they funny? Because funny people are smart :

And there's one other thing to listen for while they're yakking. The word "I" can be very telling...

Powerful people don't say it much . Less powerful people say it the most:

(To learn what Harvard research says will make you happier and more successful, click here .)

Okay, so you know when to trust your gut. Now there are a gazillion studies on behavior, so let's focus on reading people to get answers to the questions we all want to know, like...

Of course, people trying to deceive or manipulate you are going to fake signals that they are trustworthy.

So we need to focus on unconscious behaviors that aren't easily controlled and convey a clear message.

In Honest Signals: How They Shape Our World , the authors mention one to keep your eye on:

Speech mimicry and behavioral mimicry: Are they using the same words you use? Speaking at a similar speed and tone? Are they sitting the way you sit? Is a subtle, unconscious game of follow-the-leader going on? This is a sign the other person feels emotionally in sync with you. It can be faked but that's difficult to pull off across an entire conversation.

Beyond that, trust people who are consistently emotionally expressive in their body language:

These results suggest that cooperators may be more emotionally expressive than non-cooperators. We speculate that emotional expressivity can be a more reliable signal of cooperativeness than the display of positive emotion alone.

(To learn an FBI behavior expert's tips on how to get people to like you, click here .)