Cal. Business and Professions Code § 19163

All work to be performed by a custom upholsterer shall be recorded on a work order containing information required by rules and regulations adopted by the bureau and shall describe all work to be performed, all materials to be supplied, and the period within which the estimate shall remain effective. If any secondhand materials are to be supplied, the work order shall clearly identify them as secondhand. No work shall be performed and no charges shall accrue before authorization for the work and materials is obtained from the customer, and no charge shall be made for work performed or materials supplied different from those specified in the work order without the oral or written consent of the customer. One copy of the work order shall be given to the customer before any work is performed and one copy shall be retained by the custom upholsterer for at least one year. As used in this section, “materials” includes structural units, filling materials, containers, and coverings. If a copy of the work order is provided to the customer in an electronic format, an electronic copy of the work order shall be retained by the service dealer for the same retention period.