70.—Where goods of any class or description are let under a hire-purchase agreement to a dealer who deals in goods of that class or description and the dealer sells the goods when ostensibly acting in the ordinary course of his business, the sale shall be valid as if the dealer were expressly authorised by the owner to make the sale:

Provided that the buyer acts in good faith and has not at the time of the sale notice that the dealer has no authority to make the sale.