Legal Question in Business Law in California

You're kidding, right? You need to read the Talent Agencies Act beginning with section 1700 of the California Labor Code. Violation of the Act is a crime.

Talent agencies are covered extensively in California law, mainly in the Labor Code at sections 1700 to 1705.4, which is several pages of rather strict, detailed requirements placed on the talent agency business. Anyone dreaming of being in this business should read and thoroughly understand all of this material.

One of the numerous requirements is Labor Code section 1700.19(b), which requires that the talent agency's license contain "a designation of the city, street and number of the premises in which the licensee is authorized to carry on the business of a talent agency."

So, no, it is NOT legal to operate from a private mailbox address nor, for that matter, to use a post office box number.