The number one reason for a negative customer review is not listening to your customer.
Most common new customer complaint is the feeling they are being overcharged. That is almost always the fault of the service advisor not clearly communicating what would be done, why it would be done, and why it costs what it does.
Every customer is different and it is extremely important that you to learn the level of service they wish to pay for.
You MUST ensure the customer knows what the job involves and what it will cost. And if the job could escalate into added costs. You must inform them of their options when different problems are found. Setting budget limits that trigger communication about progress and findings makes sure there are no surprises!
Going above what they can afford will be the undoing of your relationship no matter how good your service is.
Over-selling or up-selling over the customers price limit will always come back to bite you...
They will never return. And you will probably get a nasty, negative review. Both will hurt your business!