Are extra fees likely and is gratuity customary?

We try to provide the best estimate based on breed and information given when setting appointments however, if the pet is larger or smaller than breed standard or the coat is matted or a significant pattern change is required incurring extra time we will advise of the new estimate on site. Further, if you choose add ons on site that estimate can be revised. Gratuity is discretionary but averages 10-20% of services.