California Code, Civil Code - CIV § 1718

(a) As used in this section:

(b) All work done by a farm machinery repair shop, including all warranty work, shall be recorded on an invoice, which shall describe all service work done and parts supplied.  If more than one act of maintenance or repair is performed by a farm machinery repair shop, the invoice shall be written in such a way that the labor cost per hour and total labor cost, as well as the specific parts used and their cost, shall be recorded on a per-job basis.

However, where work is done on an agreed total-cost-per-job basis, or the work includes an agreed total cost for component unit replacement, the invoice shall describe the work done on such basis and the total cost for such work.

(c) Each farm machinery repair shop shall give to each customer, upon request, a written estimated price for labor and parts necessary, on a per-job basis.  It shall not charge for work done or parts supplied in excess of the estimated price without the consent of the customer, which shall be obtained at some time after it is determined that the estimated price is insufficient and before the work not included in the estimate is done, or the parts not included in the estimate are supplied.  Nothing in this section shall be construed to require a farm machinery repair shop to give a written estimated price if the shop does not agree to perform the requested repair.

(d) Any violation of this section is a misdemeanor.