Yes, you should tip (unless they have a policy that specifically prohibits tipping). Think about the effort involved in cutting a person's hair. Now imagine that over an entire dog body. Even just a shave is a royal pain in the ass, because dogs, by and large, don't actually want their hair taken off. My girlfriend worked at a dog groomers for some time while she was in high school, and she has nightmare stories about dogs biting her, pulling her around, shitting on her, etc. It's not a pleasant experience, and $58 is really not that much (considering you probably won't get it done again for a long time). Give ten bucks extra. Unless you really can't afford it, in which case, screw it.