The Wealth of Nations by Part 5 Chapter 2 Page 111

tax of the same kind was proposed upon shops. The war having been undertaken, it was said, in defence of the trade of the country, the merchants, who were to profit by it, ought to contribute towards the support of it.

A tax, however, upon the profits of stock employed in any particular branch of trade can never fall finally upon the dealers (who must in all ordinary cases have their reasonable profit, and where the competition is free can seldom have more than that profit), but always upon the consumers, who must be obliged to pay in the price of the goods the tax which the dealer advances; and generally with some overcharge.

A tax of this kind when it is proportioned to the trade of the dealer is finally paid by the consumer, and occasions no oppression to the dealer.