Cal. Rev. & Tax. Code § 6046

If the marketplace facilitator demonstrates to the satisfaction of the department that the marketplace facilitator has made a reasonable effort to obtain accurate and complete information from an unrelated marketplace seller about a retail sale and that the failure to remit the correct amount of taxes or fees imposed under this part, or under any other law that imposes a fee administered pursuant to Part 30 (commencing with Section 55001), was due to incorrect or incomplete information provided to the marketplace facilitator by the unrelated marketplace seller, then the marketplace facilitator shall be relieved of liability for the taxes or fees for that retail sale. This section does not apply with regard to a retail sale for which the marketplace facilitator is the retailer selling or making the sale of the tangible personal property on its own behalf or if the marketplace facilitator and marketplace seller are related. Where a marketplace facilitator is relieved of liability for the taxes or fees on a retail sale under this section, the marketplace seller is the retailer for that retail sale.