Every time we change oil in our class C they charge us extra

Per the oil/lube & brake shop where I go they have a higher rate fro RVs, they charge me the lower regular price since I always tell them to leave my tires alone. I always check & air my tires at home. Each time I go in I need to remind them so I don't get the higher MH charge. I had to have a discussion with the owner to get this non MH pricing. Dick