With digital works I tend to not show updates because I work on things straight through most of the time, so by the time I send the lineart/sketch to you and get it approved I'd already be done with it. However, if I send you the final work and you are not pleased with it, please tell me what to fix and I will happily fix it for you. However I will only fix your commission once!. You may list several problems like "my spots aren't that color blue, they're more this blue, my wings are bat wings not bird wings and my nose is pink not black", but if I fix it for you and send it back to you, you may not say "That is fine and dandy, but I don't like the way that foot is positioned and can you put my characters hair up in a ponytail instead?" If you do not catch all of the things you want changed in the first round, all additional changes will cost extra.
However, if its something more along the lines of a color, then that is fine. Like say I got your shade of yellow wrong and its more green than gold, and even though I changed it once its still not the color you like, I can do that since all it really requires is adjusting the color balance and with a little knob turning I don't have to touch it with a digital paintbrush, but if it requires me to repaint multiple areas or redraw anything, sorry but thems the breaks, you didn't catch it the first time after I asked "are you suuuure?" I'm not going to take away fingers and add fingers and take them away because you can't decide if you like your character to have five fingers or four.
As for real media stuff, I always send updates because that's something I can't change easily, but the same thing applies. If you don't like the sketch, say so and I'll fix it, but I won't keep fixing it and fixing it so you get 20 free sketches from me. As for color, i'll try to send updates best I can but it is your responsibility to give me an accurate representation either visually or in lengthy text telling me exactly what you want, since its harder to change real media around if you forgot to mention your character has three horns on its face.
That is all.