When it appears that a trustee had been notified of the sale or assignment of a demand for which he or she would otherwise be adjudged trustee, either of the parties to the trustee process may raise the question of the validity of such sale or assignment, and the person giving notice to the trustee may be summoned as a witness and compelled to testify to the consideration upon which such sale or assignment was made. When it is found upon the evidence that such sale or assignment was not made in good faith, the trustee shall be adjudged liable as though the pretended sale or assignment had not been made.