(1) No sale made by a trustee shall be impeached by any beneficiary upon the ground that any of the conditions subject to which the sale was made may have been unnecessarily depreciatory, unless it also appears that the consideration for the sale was thereby rendered inadequate.
(2) No sale made by a trustee shall, after the execution of the conveyance, be impeached as against the purchaser upon the ground that any of the conditions subject to which the sale was made may have been unnecessarily depreciatory, unless it appears that the purchaser was acting in collusion with the trustee at the time when the contract for sale was made.
(3) No purchaser, upon any sale made by a trustee, shall be at liberty to make any objection against the title upon any of the grounds aforesaid.
(4) This article applies to sales made before or after the commencement of this Part.