I spent some time in the middle east about ten years ago and was thinking about this subject just yesterday. I keep hearing about the 'peaceful' side of Islam, but something kept nagging at me. I thought back to my time in the middle east and came up with exactly what you said--you never knew if they were telling the truth or not. Machiavelli was a piker compared to these people. The end justifying the means is a way of life for them.
That's because deceiving infidels - that would be us - is a virtue. It reminds me of the old story of the oisonous snake that bit the sympathetic young girl who had carried it across the river. When she complained, he told her, "you knew what I was when you picked me up."
So how many of our latter day "allies" will sonner or later, turn out to have been telling us short term lies?
Reagan's old adage, "trust but verify" seems good.