The Wealth of Nations by Part 4 Chapter 5 Page 73

had been allowed to keep a shop, and to sell his own goods by retail, could not have undersold the common shopkeeper. Whatever part of his capital he might have placed in his shop, he must have withdrawn it from his manufacture. In order to carry on his business on a level with that of other people, as he must have had the profit of a manufacturer on the one part, so he must have had that of a shopkeeper upon the other.

Let us suppose, for example, that in the particular town where he lived, ten per cent was the ordinary profit both of manufacturing and shopkeeping stock; he must in this case have charged upon every piece of his own goods which he sold in his shop, a profit of twenty per cent. When he carried them from his workhouse to his shop, he must have valued them at the price for which he could have sold them to a