Once I find a good barber I stick with him and usually tip 75% or more. I figure if I can tip a waitress 20% for the food she doesn't even cook, that I eat up in an hour; I sure as heck can pay a trained professional to cut my hair and tip heavy. My haircut makes me look good for several weeks.
Besides, when I walk into the barber shop they push the non tippers out of the chair and get me in toot sweet. Some days you'd think I owned the joint.