It seems simple enough: A standard tip is about 15 to 20 percent of the bill, which isn't too hard to calculate. But over the years, the rules of salon and spa tipping have become complicated. What do you do, for example, when one person washes your hair and someone else cuts it (God forbid a third person does your blowout)? What about facials at medical spas -- since when do you tip a physician? And does the old rule of not tipping the salon owner still stand?

To take the stress out of tipping, we asked two salon and spa owners all of those "what if" situations. We also consulted national etiquette expert Diane Gottsman on the proper tipping protocol when it comes to salons and spas.