How to accurately tell if someone is lying?

First, observe their narrative logic. Truthful statements are usually in chronological order, with details and emotions, and consistent throughout.
Lies are constructed backwards; they can only repeat the core sentence and are afraid to add details.
As long as you ask more questions, they will definitely contradict themselves.
Second, watch for avoidance behaviors. If they encounter a key issue, they shift the topic, deliberately get angry, question your trust in them, or change the subject—this person is 99% guilty.
Third, compare their versions over time. For the same event, ask again after a while; truthful accounts are generally consistent, while lies change each time, and they can’t even remember how they changed last time.
Fourth, see if their emotions and language match. If they say something with a lot of grievance or righteous indignation but show no facial expression, have wandering eyes, or speak with a tight voice, this is a typical sign of insincerity.
Fifth, check if they are overly self-affirming. People telling the truth tend to point out key facts and stop, while liars tend to explain desperately.