Good Question! There is no need to reinvent the wheel here. Others sites and authors have done a good job of exposing when and where Muhammad deceived people. In addition to Muhammad contradicting both Old and New Testaments, one of the best examples of his deception is when he went back on The Treaty of Hudaybiyya that he made with the Meccan Arabs. Answering-Islam does a thorough job at explaining the context and situation (an example of conduct as per Surah 33:21) in which Muhammad "lied": http://www.answering-islam.org/Silas/hudaybiyya.htm.