Check this out
How Much Should You Tip?
What customers do: In Aveda's informal poll, the lowest tip was 10 percent and the highest was 25 percent, but most women said they stick to 20. In and around big cities, the percentage was more generous, even though the services cost more. Women with supershort hair, which they get cut and colored every four to six weeks, don't always give a huge tip because their annual beauty bill is so high to begin with. Stylists in some small-town beauty shops, however, report 15 percent as the norm. Those who work in mall or drop-in hair salons, and are less likely to have a loyal clientele, sometimes get tips of even less.
Hair do's and don'ts of salon etiquette: iVillage Beauty & Style