Learning to interpret body language and avoiding transmitting unintentional signals are very good skills to have. Attempting to then manipulate someone else into trusting you with any of the more common PUA techniques like anchoring or mirroring I view as dark arts. I have read about PUA, though it was to be able to identify any techniques being used on me and not to practice them myself.

tl;dr: Studying the techniques seems useful. Actually using them to manipulate is Dark Arts.