A little over-simplistic I know but 11 quick thoughts on fibbers!
1. They change their head position quickly.
2. Their breathing changes.
3. They stand very still.
4. They repeat words or phrases.
5. They provide too much information.
6. They touch or cover their mouth.
7. They instinctively cover vulnerable body parts.
8. They shuffle their feet.
9. It becomes difficult for them to speak.
10. They stare at you without blinking much.
11. They tend to point a lot.