A common occurrence, and harder to detect:

Make no mistake: we certainly see drug seekers in the office. Many of them are charming and have extremely legitimate-sounding stories. Over the years, though, I’ve discovered something in my own thought processes that flags them unerringly: in the course of the history and exam, in which the long-suffering patient is telling a tale of such woe, such suffering, such angst, the thought occurs to me, Could this patient just be out for drugs? and I say to myself, How could you even THINK that about this nice person! That second thought is the key. More often than not, yes: that nice person is looking for drugs.