What percentage should you tip your hair stylist(whether is a high scale salon or mediocre salon, and if she's not the owner), and do you have to leave an extra tip to the girl that washed your hair?

I tip the person who cuts my hair 10-20%. In a very upscale place, I tipped the hairwasher and the consultant too. If the haircut was poorly done by a girl who talked to everyone but me and kept looking for her boyfriend out the window, I might not tip at all.