From Consumer Wiki
The sale of antiques requires a city or county business license and registration with the California Board of Equalization for collection of sales taxes. Complaints may be made to the Better Business Bureau, but the consumer may be required to seek resolution in Small Claims Court.
Board of Equalization
450 N Street
Sacramento, CA 95814
(916) 324-2397 (sales tax permit)
(800) 400-7115 (customer tax payer service)