My groomer charges $35/per dog. I have 2 dogs. I usually pay her $85. Thats a $15 tip. About 20% ... its just like anyone else who provides a service. A hairdresser, waiter, chauffer, delivery guy, etc... you tip them when they provide a service. The money they make (unless they own the business) usually goes to the business and the tips go straight to the person providing the service.
I hope that helps
