The Arabs of the Levant are much more varied in appearance than the others. One Zionist novelist, he wrote in one of his books about how the character gave up on judging by looks, after seeing too many blonde Palestinians and swarthy Jews from Germany. The Palestinians, in particular, go all the way from looking quite African, to being peachy-faced English types.
Frankly, I find telling Middle-Easterners and East Indians apart (Muslims and Hindus) because they are very similar.
However, I did once teach a group of Middle-Eastern Muslims, and waited on their tables in restaurants. Here's a dead giveaway: the way they look at women. This will work every time. There is a hateful, nasty, lustful, reptilian manner in the way a Good Muslim looks at a woman, as if she is the vilest, most disgusting creature on earth. "First I'll f*** you then I'll kill you." They looked at me that way at the head of the classroom and when I served them *alcohol*...
So, ask a chick if she has the icky shudders after he looks at her.
I don't think the best terrorist training can change this behavior, it is ingrained. When that actor (Wood something?) described how nasty the "rehearsal run" hijackers behaved toward the stewardess.