It is unlawful for a manufacturer of spirits, wine, or malt beverages holding a certificate of approval or the manufacturer's authorized representative, a distillery, brewery, or a domestic winery to discriminate in price in selling to any purchaser for resale in the state of Washington. Offering on-premises retailers different prices or a different pricing structure for wine or spirits than offered to off-premises retailers does not discriminate in price and is lawful, so long as a particular price or pricing structure for wine or spirits offered to one on-premises retailer is made reasonably available to all on-premises retailers and a particular price or pricing structure for wine or spirits offered to one off-premises retailer is made reasonably available to all off-premises retailers. Subject to and in accordance with the foregoing, price differentials for sales of spirits or wine based upon competitive conditions, costs of servicing a purchaser's account, efficiencies in handling goods, or other such bona fide business factors, to the extent the differentials are not unlawful under trade regulation laws applicable to goods of all kinds, do not violate this section.