Cal. RTC § 7373

(a) For the purpose of the proper administration of this part and to prevent evasion of the tax, unless the contrary is established, it shall be presumed that all motor vehicle fuel received at a terminal in this state, imported into this state, or refined and placed into storage for removal at a refinery in this state or blended motor vehicle fuel blended or converted in this state and no longer in the possession of the supplier has been removed or sold by the supplier.

(b) The presumption shall not apply if the supplier proves to the satisfaction of the board that both:

(1) The supplier has exercised ordinary care in entrusting control or possession of the motor vehicle fuel to another person.

(2) The person to whom the supplier has entrusted the control or possession of the motor vehicle fuel as bailee, consignee, employee, or agent, caused a removal or sale by the act of converting to that person’s own use the motor vehicle fuel so entrusted to that person by the supplier.

(c) If the supplier proves to the satisfaction of the board, the existence of both of the circumstances in paragraphs (1) and (2) of subdivision (b), then the person who converted the motor vehicle fuel to his or her own use, as well as any other person receiving that motor vehicle fuel with the knowledge that it was so converted, shall be liable for payment of the tax imposed upon that removal or sale, and all of those persons shall be considered as suppliers for the purpose of Chapter 5 (commencing with Section 7651) or Chapter 6 (commencing with Section 7851) of this part.