What is the burden of proving that a client's understanding and understanding of an attorney-client transaction was fully understood?

When an attorney-client transaction is involved, the attorney bears the burden of showing that the dealings between the parties were fair and [44 Cal.3d 373] reasonable and were fully known and understood by the client. ( Clancy v. State Bar, supra, 71 Cal.2d 140, 146-147, 77 Cal.Rptr. 657, 454 P.2d 329.) The record here does not clearly reveal the understanding of the parties with respect to the transaction. The original investment was secured by a note and deed of trust signed by White, but the value of this security was not established at the hearing. Accordingly, petitioner has not carried his burden of demonstrating the fairness of the transaction.