Islam's attitude towards lying and honoring agreements with non-Muslims. This conclusion is taken from "The 4th Conference of Islamic Research" at Al Azar University in Cairo, 1970. The teachings at Al Azar University is normative for all Sunni Muslims. For Shiites it is Qum in Iran.
Taqiyya
The expression taquija means to dissimulate and is used when serving the propagation of Islam or benefitting a Muslim compared to 'infidels'. Lying to 'infidels' is officially acknowledged and is religiously motivated.
Lying is okay
In essence taqija means that a Muslim is allowed to hide his or her intentions in a difficult situation. For instance in regard to Koran interpretations, the more mellow verses are emphasized towards people with no thorough knowledge of the matter, and threatening, harsh verses are hidden.
Muhammed did it
Taqiyya was practised by the Prophet, Mohammed, himself; in negotiations where he fooled his opponents. For that very reason Muslims often enter into agreements intending to break them when they have assumed control of the situation.
Denial
Active Muslims in the West deny the use of taqija. This emphatic denial of using taqija towards us and the authorities is part of the method used in taqiyya. Often it leads to confusion on behalf of us and negotiating authorities e.g. the Ministry of the Interior.
Common claim
A common example of taqiyya is the claim that Islam does not do missionary work in the West. At the same time Arab states spend four to five billions of Kroners to missionary work in Europe per year. In Germany 1000 of mosques have been built over the last 15 years.
Fraud is legitimate
Fraud and lies are religiously permitted means in Islam. A negotiated settlement or an agreement with a Muslim is never final.
Neither is a business contract as I found out the hard way. "Its out of scope!" "But it is the will of Allah, and either you do it or you're out of the country." What a way to do business.