California Code, Government Code - GOV § 15641

In order to verify the information furnished to the assessor of the county, the board may audit the original books of account, wherever located, of any person owning, claiming, possessing, or controlling property included in a survey conducted pursuant to this chapter if the property is of a type for which accounting records are useful sources of appraisal data.

No appraisal data relating to individual properties obtained for the purposes of any survey under this chapter shall be made public, and no state or local officer or employee thereof gaining knowledge thereof in any action taken under this chapter shall make any disclosure with respect thereto except as that may be required for the purposes of this chapter.  Except as specifically provided herein, any appraisal data may be disclosed by the board to any assessor, or by the board or the assessor to the assessee of the property to which the data relate.

The board shall permit an assessee of property to inspect, at the appropriate office of the board, any information and records relating to an appraisal of the assessee's property, including “market data” as defined in Section 408 of the Revenue and Taxation Code.  However, no information or records, other than “market data,” which relate to the property or business affairs of a person other than the assessee shall be disclosed.

Nothing in this section shall be construed as preventing examination of that data by law enforcement agencies, grand juries, boards of supervisors, or their duly authorized agents, employees, or representatives conducting an investigation of an assessor's office pursuant to Section 25303, and other duly authorized legislative or administrative bodies of the state pursuant to their authorization to examine that data.