I think it would have to do with who the customer is. Mr. Powers has 5 vehicles that I service. He comes to me with a check engine light on, I will read it for free because he has spent thousands of dollars with me and will be back and he will send customers my way. Mrs. Jones who was referred to me by her friend at the beauty shop and her check engine light is on and I have never seen her vehicle before, I will quote a diagnostic fee.