Here in Germany it is custom to tip 10% to hairdressers, service staff, even a handyman expects something. State employees are not allowed to accept tips. That includes the postman.
My hairdresser is the owner, but he has ridiculously cheap prices, €13 for hubby and €15 for me. We usually give about €4 tip for the 2 of us. He does all the work himself. We wash our hair beforehand, and don't need a blowdry except in frosty weather, but he insists on a little styling.
In other salons, the minimum charge would be around €25 upwards, and they usually try to sell extra things, like gel or mousse. I prefer using a shampoo bar and no conditioner. I do not like all these brand names with so many toxic chemical ingredients, the shorter the list, the happier I am.