California Code, Probate Code - PROB § 16463

(a) Except as provided in subdivisions (b) and (c), a beneficiary may not hold the trustee liable for an act or omission of the trustee as a breach of trust if the beneficiary consented to the act or omission before or at the time of the act or omission.

(b) The consent of the beneficiary does not preclude the beneficiary from holding the trustee liable for a breach of trust in any of the following circumstances:

(c) Where the trustee has an interest in the transaction adverse to the interest of the beneficiary, the consent of the beneficiary does not preclude the beneficiary from holding the trustee liable for a breach of trust under any of the circumstances described in subdivision (b) or where the transaction to which the beneficiary consented was not fair and reasonable to the beneficiary.