I have some magician/"psychic" friends, and so much of that is cold reading (which is pretty much what Sherlock does) and other Dark Arts.

In case people haven't heard of it:

Cold reading is a series of techniques used by mentalists, psychics, fortune-tellers, illusionists, and con artists to determine or express details about another person, often in order to convince them that the reader knows much more about a subject than they actually do.[1] Without prior knowledge of a person, a practiced cold reader can still quickly obtain a great deal of information about the subject by analyzing the person's body language, age, clothing or fashion, hairstyle, gender, sexual orientation, religion, race or ethnicity, level of education, manner of speech, place of origin, etc. Cold readers commonly employ high probability guesses about the subject, quickly picking up on signals from their subjects as to whether their guesses are in the right direction or not, and then emphasizing and reinforcing any chance connections the subjects acknowledge while quickly moving on from missed guesses.

-From wikipedia