Cal. Rev. & Tax. Code § 8732.5
A vendor is relieved from liability to collect use fuel tax which became due and payable subsequent to July 1, 1958, insofar as the sales of the fuel are represented by accounts which have been found worthless and charged off for income tax purposes. If the vendor has previously paid the amount of the tax, he may, under rules and regulations prescribed by the board, take a credit in such amount. If any such accounts are thereafter in whole or in part collected by the vendor, the gallons of fuel represented by the amounts collected shall be included in the first return filed after such collection and the amount of the tax thereon paid with the return. The board may, at its option, require the seller to submit periodical reports listing accounts delinquent for a 90-day period or over.
Ca. Rev. and Tax. Code § 8732.5