Section 15. The provisions of sections thirteen to twenty-one, inclusive, shall not apply to sales at retail or sales at wholesale made:—(a) in an isolated transaction and not in the usual course of business; (b) where cigarettes are advertised, offered for sale or sold in bona fide clearance sales for the purpose of discontinuing trade in such cigarettes and said advertising, offer to sell or sale shall state the reason therefor and the quantity of such cigarettes advertised, offered for sale or to be sold; (c) where cigarettes are advertised, offered for sale or sold as imperfect or damaged and said advertising, offer to sell or sale shall state the reason therefor and the quantity of such cigarettes advertised, offered for sale or to be sold; (d) where cigarettes are sold upon the complete final liquidation of a business; (e) where cigarettes are advertised, offered for sale or sold by any fiduciary or other officer acting under the order or direction of any court; (f) where cigarettes are advertised or offered for sale or sold for charitable purposes or to relief agencies; (g) where cigarettes are sold on contract to any department, board or commission of the commonwealth or any political subdivision thereof, or to any institution maintained thereby.