If it helps with what others are describing:
Plaster should be smooth to the touch. No pock marks or "moon craters" of any kind. No scratches or trowel marks or foot prints or sharp ridges.
But if you shine a light across a plaster surface, like from a pool light, you'll see that it is not flat. It is applied by hand, not with a machine or screed, and the application is subject to the skill of the plasterer. But even the best of them cannot make the surface "laser-level" flat. You'll see some subtle hills and valleys that are exaggerated by the shadows caused by the low angle of a pool light at night. And that affect is greatly lessoned, or completely eliminated from view, during the day, when the light is coming from above and ambient light is reflecting all around, eliminating the shadows. Generally speaking, you cannot feel these hills and valleys with your feet as you walk on them, unless you are really trying to. They won't be pronounced.
Perfectly smooth to the touch, but not perfectly flat to the eye.
That picture in post #5 looks to be the work of someone that is not at all good at their craft. That's not just the shadow affect, or a water balance issue (though both could also be at play). That is primarily just poor workmanship, and I wouldn't accept it in my pool. The pock marks, ridges, gouges, trowel marks... nope. The other glaring red flag: "He was in the pool on the new plaster trying to smooth out the areas around the mosaics..." A skilled plasterer does not need to come back the next day to fix up or smooth out his work. Plaster is best applied all at once, before any of it cures, not patched up at a later date, layer on layer.