Policy of honesty:
Their is no quick fix solution for dealing with dishonest person. If however an answer is sought in one word, it would be: Honesty. Yes, do not become dishonest only to deal with dishonest person. It is not a moral advise but a practical one. A person who is a practising dishonest can not be out tricked by an amateur just turned dishonest without any experience of deception and deceit. So stick to the known policy of honesty. In fact honesty has a leverage.