It is unlawful for any person, firm or corporation to sell or offer for sale at retail, for use or consumption in any motor vehicle, or to deliver into any motor vehicle, for actual apparent use therein, any product whatsoever for use in supplying, creating or generating motive power to the motor vehicle, or lubricating oil for the motor vehicle, at any price or prices, except the exact price or prices contained on the sign or placard required by this chapter, or to offer, deliver, grant, allow, give or promise, any actual, prospective, contingent, immediate or future benefits, concessions, discounts, refunds, premiums or gratuities of any kind or nature, that, in any degree, manner or extent, shall, or be calculated or intended to, effect or accomplish a sale of the product for other than the posted price or prices.