How to Spot a Liar
Humans evolved for social interaction, right? And lies and manipulation are common in social life, right? So you'd think that humans would be pretty sophisticated at detecting deception and resisting manipulation. But from my casual observation, they aren't. A huge number of people are mind-bogglingly gullible and easily manipulated.
You may already be thinking of the most salient recent illustration of this: the fact that literally the most obvious scammer that I have ever seen has been elected to the highest public office in the land, over many other candidates, and has inspired millions of fanatical followers who hang on his every lie. But there are many other examples. E.g., consider people who join the church of Scientology. Or consider when someone sues the government, and the government argues that it can't be required to provide discovery because the information needed by the plaintiff would "compromise national security" -- and some people actually believe them. Or consider when industry insiders support a regulation for their industry on the grounds that it will help protect the consumer from the industry -- and millions of consumers buy it and start demanding the regulation. Or consider when a politician running for office runs a negative campaign ad against his opponent -- and people just accept the ad at face value, as if it was an objective news report.
I'm not going to go into those cases. That's just to illustrate the sort of thing that I find mind-boggling. Sometimes, it seems as if half the population (despite lying all the time themselves) has never conceived the possibility that another person can lie.
Anyway, these are my tips on how to identify a liar. Since people are so bad at it, they need these tips.
But first, some BS ideas that don't work: You cannot tell if someone is lying by looking carefully at their face, or listening carefully to their voice. There are psychological studies on this that verify that, while people think they can identify lies in this way, they cannot. For example, you cannot tell by watching Brett Kavanaugh whether he is telling the truth, by looking at whether he seems sincere. Also, people do not have "tells", like scratching their ears whenever they lie, or whatever (as is sometimes portrayed in movies).
Here are the real keys to identifying liars, as far as I can figure, based on personal observation and reflection.
Independent sources: This is obvious, but it is the main way of identifying liars: if a person says things that conflict with information from independent (reliable) sources, then that person is probably a liar.
Corollary: if you're not sure whether person S is to be trusted, pick some factual claim S makes that is easily verifiable or refutable, and look it up. If S lies (or is wrong) about that, then S probably lies (or is wrong) about a lot of the things that you haven't checked on.
If you know that S lies to other people (e.g., because S has told you about these lies), then you should assume that S lies to you too.
Intrinsic implausibility: If S frequently says things that have very low prior probabilities, then S may be a liar (or just bad at thinking).
Inconsistency: Changing one's story, especially when the audience starts to question that story or acquires new information undermining the old story, is a sign of dishonesty.
Ulterior motives: If S says something that S would have an obvious motive to say even if it was not true, then you have to consider that S may be lying. In this category, it is especially likely to be a lie that (a) the person you are talking to has an incredibly high amount of some desirable trait (intelligence, wealth, etc.), (b) you will gain some incredible benefit from giving money, or some other thing of value, to the person you are talking to. (E.g., "if you give money to me, then God will give you ten times as much money later".)
Too good to be true: If S regularly says what you want to hear, or what an observer would likely think that you want to hear, then S is probably a liar. Reality is not systematically biased toward your interests; therefore, a truth-teller will frequently give you bad news.
Lack of qualification: Reality is usually complex. Therefore, people who are concerned about truth usually make qualifications. People who make simple, very strong, highly confident generalizations are commonly either lying or just bad at thinking. For example, "All generalizations are false."
Dishonest profession: There is an old joke: "Q: How can you tell when a politician is lying? A: His lips are moving." It works for lawyers, too, and advertisers -- all professions whose main job qualification is the ability to manipulate people. If S belongs to a dishonest profession, then S is likely dishonest.
Lack of Detail: When a person is telling the truth, there will typically be a large number of details that the person can supply immediately. But when they make up a story, a person will have difficulty coming up with details on the spot. So if you have a chance to question someone, one way of testing veracity is to ask a series of detailed questions in sequence. (But note that most people forget details that they don't care about quickly. E.g., if you met a friend earlier today, you probably don't now know what they were wearing.)
Stalling for time: As a result of the previous point, when asked questions about a false story, people stall for time. They will answer slower than normal. They might, e.g., repeat the question, in order to gain time to invent an answer. But professional liars (such as politicians) will be smoother; they will just launch seamlessly into evasion, which brings me to the next item.
Evasion & distraction: This isn't really lying, but something in the neighborhood: when asked a question, one gives an "answer" that does not answer the question. This is extremely common among politicians. Virtually all of their answers are like that.
Exercise for the reader: watch an interview, debate, or press conference with any politician(s). Identify all the yes/no questions that are asked. Of those questions, count the number of responses that contain either "yes", "no", or "I don't know". Prediction: the number will be zero.
This tactic works surprisingly well, because most voters are too stupid to remember a question that they heard fifteen seconds ago in order to compare it to the "answer" they are now hearing.
A particularly important special case of this tactic: when someone is accused of a crime or other wrongdoing, they don't address the charge but instead just attack their presumed enemies, attack the questioner, or attack the other political party.
This is similar to the ever-popular whataboutism: when confronted with an argument or issue that you can't or don't want to address, ignore the issue and just attack your political opponents.
A bit more generally, to avoid having to answer a question, people will sometimes just say stuff to stir up a bunch of emotions. That often distracts listeners and makes them forget whatever was the original topic.
When someone gives evasive answers, assume that they are probably doing it on purpose, and then think about the most likely explanation for their not wanting to answer the original question. That often helps uncover other deceptions.
Inappropriate confidence: Practiced liars do it with confidence. Scammy sales people will stare directly at you while spewing a rehearsed script. This is because they think that "looking you in the eye" is a sign of sincerity, and they are trying to send you a false signal of sincerity. (Normal people do not stare you in the face continuously while talking. Normal people just occasionally look at you to make sure you're still listening.) Humans have a very crude instinctive heuristic for judging credibility: "the more confident the speaker sounds, the more likely his statement is to be true." And with normal people that heuristic works kind of okay. Long-time liars, however, exploit this heuristic by regularly projecting maximal confidence in all of their lies. Besides staring you in the eye, they'll talk loudly, forcefully, and continuously, using strong language. (Ex.: see President Trump.)
The dumb heuristic is this: "If S seems more confident when saying P than most people are when speaking, then P is probably true."
A better heuristic would be this: "If S seems more confident when saying P than S usually does when speaking, then P is probably true."
People who are habitually overconfident are probably unreliable and dishonest.
Too much agreement: Intelligent and independent thinking people typically disagree a fair amount with other people. Therefore, if you meet someone who constantly appears to agree with whatever views are popular in their social group, there is a good chance that they are lying (or else they are dumb or a blind follower).
The above points are not exactly amazing discoveries -- most of that is very obvious. That's why I am amazed that so many seem blissfully (or miserably?) unaware of them. I'm amazed, for example, that "prosperity gospel" preachers get rich, just by telling their congregants that if they give money to the preacher, God will reward them. I mean, it'd be hard to think of a more obvious scam.
Now, I know that most people are dumb, but you would expect them to have some sort of evolved "cheater-detection" instincts that would catch at least the very most obvious lies.
In the case of politicians, part of the problem is that talking about politics lowers people's IQ by about 30 points; it's like an instant lobotomy. So if some political figure or commentator is, or pretends to be, on "your side" politically, then suddenly you become the most naive mark.
In conclusion: try not to be mind-bogglingly gullible.