Still body posture
The body posture of someone trying to deceive you may be stiller as they are trying to control any non verbal signs that may give them away.
Response times
If you know the person, watch for more hesitations and longer responses times as their mind races to maintain the fiction.
Listen for how they say things
The person trying to deceive you will try to say as little as possible so that they won't be caught out. If you know the person well, you may notice that they will try to limit their answers to a simple yes or no. Also, the individual may use less specific language.
Eye contact
You are probably familiar with the averted eye contact of the deceiver but research has also identified more blinking and dilation of pupils. But you will have to be watching very closely to notice this.
Fidgeting
Adaptors, those gestures such as flicking hair, fiddling with pens or other nervous self touching gestures tend to increase with those trying to deceive you.
Displays of emotion
People trying to deceive you are likely to smile less and may seem less friendly or attentive.
