No dealer shall be convicted of a violation of the provisions of this chapter when he can establish a guaranty signed by a wholesaler, jobber, manufacturer or other party residing in the United States, from whom he received in good faith such articles, to the effect that the same in original or unbroken packages is not adulterated or misbranded within the meaning hereof, unless it shall appear that such dealer knew the same to be in fact adulterated or misbranded within the meaning hereof. The provisions of this section shall not apply in the case of food and drugs, devices and cosmetics, subject to deterioration if the court finds that the adulteration has occurred after delivery to, and has resulted from negligence on the part of, the dealer.