Need advice on a customer

At IBM we used to have a saying: "The customer is King. He makes payday's possible".

You can do the work, or not, but as business owner, and especially in your trade, your job is to build the car to the customer's specification. It's his car, it's his money, and it's his wishes.

The way to handle this, is to advise the customer of your opinion, once. If he agrees, fine, but, if he doesn't agree, your opinion of his car no longer matters. At that point you can decide if you want to be a businessman and build it to the customer's specifications, or be a puritan and pass the work to another shop.

Understand, if he want's it done, he's going to get it done with you, or without you. He controls what gets done to his car. You control whether you will be the one to do it, or not.