What is the interpretation of the Prophet's saying, "He who deceives us is not of us"?

Deception is when a seller falsely presents a perfection in his merchandise or conceals its defect, and it is the opposite of sincerity. It takes many forms, including the deception of a ruler towards his subjects, deception in sales and transactions, deception in advice, deception in industry, and deception in marriage. The Prophet's saying, "He is not of us," means that he is not upon our path or methodology, and he is not among those guided by our guidance and who emulate our knowledge, our actions, and our righteous way.