No drug retailer shall sell any drugs, medicines, cosmetics, toilet preparations or drug sundries at a price below the manufacturer’s wholesale list price per dozen; nor, in the case of biologicals or other of the above-mentioned products which are not customarily sold in dozens or greater lots, sell such products at less than the manufacturer’s wholesale list price per unit. Notwithstanding the provisions of the preceding sentence, any drug retailer may sell at less than the prices specified above, imperfect or actually damaged merchandise or bona fide discontinued lines of merchandise, if advertised, marked and sold as such; merchandise sold upon the complete final liquidation of any business; merchandise sold or donated for charitable purposes or to unemployment relief agencies and drugs or drug sundries sold to physicians, dentists, veterinarians or hospitals, but not for the purpose of resale by them.