The bootlegger salesmen
As in many other businesses, such as cash registers, vacuums, brushes, and scores of others, the bootlegging syndicates employed salesmen to promote their wares. These salesmen carried samples with them, concealed often in compartmented cases which appeared at first glance to contain other products pertinent to the business they were visiting. A salesman visiting a restaurant might have carried samples of flatware or dishes, for example, or one visiting a drug store may carry patent medicines, concealing the booze beneath.
The bootleggers quickly learned that their customers wanted the genuine beverages which had been available before Prohibition, and their sample cases contained them. In reality, fine Scotch Whiskies were becoming increasingly rare and difficult to obtain. Smuggling did occur, on a grand scale, through Canada, and from Cuba. Smuggling brought with it inherent risks since it involved eluding the Coast Guard and the customs agents in the United States, and the Royal Canadian Mounted Police north of the border.
This meant that the salesmen often presented the genuine article for sampling and sale, but the delivered order was alcohol converted to resemble the real stuff with flavorings and coloring, presented in the appropriately shaped bottles and with genuine labels affixed to them. One New York bootlegger boasted that in his several years in the business he had never received a complaint regarding the quality of his products, none of which were the genuine article which his customers thought they were consuming.