Any sale of the assets of an estate by the executor or administrator shall be made at public auction, after reasonable notice of the sale, or by private sale under the advice and direction of the probate court, provided that this advice and direction shall not be required in the case of a sale at private sale by an executor or an administrator with the will annexed in the exercise of a power to sell at private sale conferred on him or her by the will. A private sale, unless authorized by the probate court or by the will, or a sale by auction improperly made, shall be deemed maladministration.