California Probate Code § 16004.
(a) The trustee has a duty not to use or deal with trust property for the trustee’s own profit or for any other purpose unconnected with the trust, nor to take part in any transaction in which the trustee has an interest adverse to the beneficiary.
(b) The trustee may not enforce any claim against the trust property that the trustee purchased after or in contemplation of appointment as trustee, but the court may allow the trustee to be reimbursed from trust property the amount that the trustee paid in good faith for the claim.
(c) A transaction between the trustee and a beneficiary which occurs during the existence of the trust or while the trustee’s influence with the beneficiary remains and by which the trustee obtains an advantage from the beneficiary is presumed to be a violation of the trustee’s fiduciary duties. This presumption is a presumption affecting the burden of proof. This subdivision does not apply to the provisions of an agreement between a trustee and a beneficiary relating to the hiring or compensation of the trustee.