Knocking the puck out and checking for channels, stirring the espresso. All before it's served.

We do that indeed. Apart from good distribution technique and the impossible of tasting every single shot before serving it, this is my last quality control check before serving. Even if the distribution and locking the portafilter into the group may look perfect, and the shot time and yield went according to plan, checking the puck integrity and seeing no channels after extraction is a crucial step for me. And then I'm aware of the fact that most of the customers don't stir the espresso and drink it as it was served. To connect all the layers of espresso, I gently stir it for them before serving the coffee. The flavors are then much more in balance. Without stirring, one gets the bitter crema from the top at first, then the pleasant liquid and the bottom, which is sour (just like it goes during extraction of the espresso).