New law, Assembly Bill 1888, repeals the right of a principal to demand that the transfer tax be shown on a separate piece of paper. This law comes into effect on January 1, 2015. Previously, a seller or buyer of real property could demand from the county that the documentary transfer tax (the DTT) be stated apart from the recorded document. This enabled some principals to effectively keep the purchase price secret, since the amount of the transfer tax can be reliably used to deduce the purchase price. (Although the information could be obtained through a California Public Records Act request.) Now every document subject to the DTT when it is submitted for recordation must show on its face the amount of the tax due. These rules have little impact on listings input into an MLS since MLS Model Rules require the reporting of the selling price within two days after the final closing.
In this link please find an explanation of Documentary Transfer Tax and the Southern California counties Transfer Tax Rates.