Muslims approach transactions with the stance that the other guy is always out to take advantage of them. A muslim must always be forceful and bullying in any transaction or he will be perceived as weak and not a worthy adversary. Lying and getting away with it demonstrates strength. That is why they respect murderous tyrants like Mohammed.
That is why they are incompatible with western culture which enters into transactions with respect, honesty,and a cooperative approach instead of combative.