One easy and quick way to see if someone is potentially telling you a lie is to look at the articles “a”, “an” (indefinite articles)and “the”(definite article). When someone first introduces something into a story, such as a knife, the article “a” (or “an”) should precede it. If they start the story with “the”, they might be fibbing. For example: “A man approached me with a knife in his hand” vs “The man approached me with the knife in his hand”. The first sentence is the correct way to introduce the event, the second one assumes you are already familiar with the “man” and “knife”. If the speaker/writer has not already introduced the “man” and “knife”, they are likely not drawing the story from memory.
Keep in mind, however, that some items are understood to be already familiar to the listener/reader because there is only one of them (McClish, 2012). Items such as post office, police station, etc usually don’t need to be introduced, so using the definite article “the” with these is ok.