California Code, Business and Professions Code - BPC § 9795

All work done by a repairperson, including all warranty work, shall be recorded on an invoice and shall describe all work done and parts supplied.

Work and parts shall be listed separately on the invoice, which shall also state separately the subtotal prices for work and for parts, not including sales tax, and shall state separately the sales tax, if any, applicable to each.

If any used, rebuilt, or reconditioned parts are supplied, the invoice shall clearly state that fact. If a part of a component system is composed of new and used, rebuilt, or reconditioned parts, the invoice shall clearly state that fact.

One copy of the invoice shall be given to the customer and one copy shall be retained by the repairperson.