how to anticipate behavior,practice i would say is the best and maybe only way.police and Docs seem be good at it because of all the people they come in contact with in their work,plus i would say in different parts of the county behavior is not the same enough to really tip you off to what comes next in a face to face.
all i can say is that in the years i worked with people at a hospital i,and my fellow workies,could watch someone cross a waiting room on a late friday night and say "drug seeker"or whatever.