This will be the first of my postings that are tagged "tools for living".
If you suspect someone is lying, you can ask them, with loving interest, to "tell me how that was" for them. Tell more details, and how it made them feel. One should only ask this question when NOT fully convinced the person is lying, and only if the reason you are asking is a kind one. It is a well-worn technique for finding out the truth, but done in kindness, it is a gift to the lie-teller. When it is done in true loving kindness, the untruth might be undone.
I don't want to use that term, "lie-teller" any more. I will substitute "Untruth-teller". A person doesn't always know when they are telling an untruth. And, the deepest part of every person never lies - it can't. If you pay attention to the deepest part of yourself and others, you will see only the truth about people.
In our as-currently-constructed everyday world, though, sometimes people believe they are lying. They try to lie. If you ask them for their own emotional reactions to the story they are telling, they are likely to be come aware of that intention. Some truth or other is likely to become apparent to both of you.
Warning: Only use this technique when you are in a positive, loving state. It is NOT necessary to get the person to admit to lying, for the truth to become apparent. Controlling or manipulating the person is not the point. Don't use it for trivial lies, or loving untruths.