A factor must obey the instructions of his principal to the same extent as any other employé, notwithstanding any advances he may have made to his principal upon the property consigned to him, except that if the principal forbids him to sell at the market price, he may, nevertheless, sell for his reimbursement, after giving to his principal reasonable notice of his intention to do so, and of the time and place of sale, and proceeding in all respects as a pledgee.