It shall be unlawful for any person engaged in commerce, in the course of such commerce, either directly or indirectly, to discriminate in price between different purchasers of commodities of like grade and quality, where either or any of the purchases involved in such discrimination are in commerce, where such commodities are sold for use, consumption, or resale within this state, and where the effect of such discrimination may be substantially to lessen competition or tend to create a monopoly in any line of commerce, or to injure, destroy, or prevent competition with any person who either grants or knowingly receives the benefit of such discrimination, or with customers of either of them; provided, that nothing herein contained shall prevent differentials which make only due allowance for differences in the cost of manufacture, sale, or delivery resulting from the differing methods or quantities in which such commodities are to such purchasers sold or delivered; provided further, that nothing herein contained shall prevent persons engaged in selling commodities, wares, or merchandise in commerce from selecting their own customers in bona fide transactions and not in restraint of trade; provided further, that nothing herein contained shall prevent price changes from time to time where in response to changing conditions affecting the market for or the marketability of the commodities concerned, including, but not limited to, actual or imminent deterioration of perishable commodities, obsolescence of seasonal commodities, distress sales under court process, or sales in good faith in discontinuance of business in the commodities concerned. Nothing herein contained shall prevent a seller rebutting the prima facie case thus made by showing that his or her lower price to any purchaser or purchasers was made in good faith to meet an equally low price of a competitor.