This is a thread to work toward a summary of "General principles of deception detection." At this point the purpose of the thread would be to collect and comment on good sources which discuss techniques for detecting deception. The thread can go in many directions but largely in the spirit of this from Lucian's "Alexander the Oracle Monger," to collect advice and methods for evaluating credibility and detecting fraud:
And at this point, my dear Celsus, we may, if we will be candid, make some allowance for these Paphlagonians and Pontics; the poor uneducated “fat-heads” might well be taken in when they handled the serpent—a privilege conceded to all who choose—and saw in that dim light its head with the mouth that opened and shut. It was an occasion for a Democritus, nay, for an Epicurus or a Metrodorus, perhaps, a man whose intelligence was steeled against such assaults by skepticism and insight, one who, if he could not detect the precise imposture, would at any rate have been perfectly certain that, though this escaped him, the whole thing was a lie and an impossibility.
and this from Lucretius Book One:
You may, Yourself, some time or other, feel like turning Away from my instruction, terrified By priestly rant. How many fantasies They can invent to overturn your sense Of logic, muddle your estates by fear! And rightly so, for if we ever saw A limit to our troubles, we'd be strong, Resisters of religion, rant and cant, But as things are, we have no chance at all With all their everlasting punishments waiting us after death.
For example, the United States Ninth Circuit has this list of instructions given to jurors in evaluating the credibility of witnesses in criminal cases: https://www.ce9.uscourts.gov/jury-instructions/node/343
3.9 CREDIBILITY OF WITNESSES
In deciding the facts in this case, you may have to decide which testimony to believe and which testimony not to believe. You may believe everything a witness says, or part of it, or none of it.
In considering the testimony of any witness, you may take into account:
(1) the opportunity and ability of the witness to see or hear or know the things testified to;
(2) the witness’s memory;
(3) the witness’s manner while testifying;
(4) the witness’s interest in the outcome of the case, if any;
(5) the witness’s bias or prejudice, if any;
(6) whether other evidence contradicted the witness’s testimony;
(7) the reasonableness of the witness’s testimony in light of all the evidence; and
(8) any other factors that bear on believability.
Sometimes a witness may say something that is not consistent with something else he or she said. Sometimes different witnesses will give different versions of what happened. People often forget things or make mistakes in what they remember. Also, two people may see the same event but remember it differently. You may consider these differences, but do not decide that testimony is untrue just because it differs from other testimony.
However, if you decide that a witness has deliberately testified untruthfully about something important, you may choose not to believe anything that witness said. On the other hand, if you think the witness testified untruthfully about some things but told the truth about others, you may accept the part you think is true and ignore the rest.
The weight of the evidence as to a fact does not necessarily depend on the number of witnesses who testify. What is important is how believable the witnesses were, and how much weight you think their testimony deserves.