If a purchaser of a vehicle pays to the dealer an amount for the licensing or transfer of title of the vehicle, which amount is in excess of the actual fees due for such licensing or transfer, or which amount is in excess of the amount which has been paid, prior to the sale, by the dealer to the state in order to avoid penalties that would have accrued because of late payment of such fees, the dealer shall return such excess amount to the purchaser, whether or not such purchaser requests the return of the excess amount.
Source:
Section 11713.4, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=VEH§ionNum=11713.4..