California Code, Revenue and Taxation Code - RTC § 6006.6

“Sale” includes any sale at an auction in respect to tangible personal property which is sold to a successful bidder at the auction upon an agreement or understanding at the time of the sale that the property involved either will not be delivered to the successful bidder or that any amount which he may pay for the property pursuant to the sale will be returned to him. The tax shall be computed in such case upon the amount of the successful bid.