the obvious answer is attitude and providing the services advertised, with enthusiasm as a bonus.
That said, as you pointed out, sometimes you just want the visual memories of a fit as fuck hottie riding you senseless :p also, we all select SP's based on our personal tastes and the images available, and thus, in theory, you shouldn't find yourself in a punt with someone that is not your type, service level is what this site can help you tie together with your selections.