This is a round-up video of the two semi-final matches of the 2013 Netsuit Open in San Francisco. It's worth to watch every second of it but I would like to point out two shots that demonstrate a type of deception that all advanced/pro players use to a certain extent, but nobody more expressively as Gregory Gaultier (and in previous times, the other great French player, Thierry Lincou):
it's the head-turning deception, when you, simultaneously to hitting the ball, turn your head in the opposite direction of where you in fact are going to hit the ball. In the below video, Gaultier does it on the volley at 0:14. There is also an almost totally identical version of this shot at 4:54 by Ramy (against James Willstrop). And if you prefer seeing how this deception looks like when played not on a volley, but on a drive, then go to 3:58 (even if James, this time, was not confused by it).
So which is the right time/situation to use this type of deception?
I think you need two things coming together in front of the court. 1) your opponent's shot must be loose off the sidewall to make the deception of a straight shot really threatening. 2) you shouldn't be on an extreme stretch as you need some extra hold/delay on your shot to send your opponent towards the direction your are turning your head to. Oh, and finally, strong neck muscles are an advantage as well.