Would you care to re-phrase your question?
Also as to Rojo's big relativistic point, yes your bias will distort your perception BUT regardless of someone's perception, there is an underlying truthful answer to the question.
"Is he a liar on not?"
EVERY SINGLE HUMAN BEING ABOVE THE AGE OF 2 YEARS OLD IS A LIAR (probably most who are under 2 are as well, though it is a bit harder to pin them down). As a result, your question, "Is he a liar or not?" is equivalent to asking, "Is he a member of a set of beings WHICH CONTAINS THE ENTIRE ADULT HUMAN POPULATION as a subset?"
Again, care to re-phrase?