(1) Save as hereinafter provided in this section, it shall be no defence in a prosecution under this Act to prove merely that the accused was ignorant of the nature or quality of the insecticide in respect of which the offence was committed or of the risk involved in the manufacture, sale or use of such insecticide or of the circumstances of its manufacture or import.
     (2) For the purposes of section 17, an insecticide shall not be deemed to be misbranded only by reason of the fact that--
     (a) there has been added thereto some innocuous substance or ingredient because the same is required for the manufacture or the preparation of the insecticide as an article of commerce in a state fit for carriage or consumption, and not to increase the bulk, weight or measure of the insecticide or to conceal its inferior quality or other defect; or
     (b) in the process of manufacture, preparation or conveyance some extraneous substance has unavoidably become intermixed with it.
     (3) A person not being an importer or a manufacturer of an insecticide or his agent for the distribution thereof, shall not be liable for a contravention of any provision of this Act, if he proves--
         (a) that he acquired the insecticide from an importer or a duly licensed manufacturer, distributor or dealer thereof;
         (b) that he did not know and could not, with reasonable diligence, have ascertained that the insecticide in any way contravened any provision of this Act; and
         (c) that the insecticide, while in his possession, was properly stored and remained in the same state as when he acquired it.