I'm asking specifically about Adam Smith and his book the Wealth of Nations. It is said that he was responsible for first describing the theory of modern capitalism, but I'm wondering how that distinction is made when people were free to freely trade and accumulate wealth before then. I'm aware of mercantilist policies that may have limited international trade, but on street level, weren't most people free to set their own prices and production before Wealth of Nations was published? So the question really is what did he write that was so revolutionary that it is considered the basis of modern capitalism.
Actually, many goods in the 18th century Anglosphere were constrained by various price controls. Foodstuffs, in particular, had a fair price set by some level of government or another (depends when and where you're looking), and charging more than the set price could get a person fined... if an angry mob didn't torch their business or rip them to shreds first.
Government-granted monopolies also played a huge role. One of the factors leading to the Boston Tea Party was the British crown granting a monopoly over tea sales in America to the British East India Company. Many British elites were heavily invented in the EIC, so they got governmental support in a way others didn't.
While free trade existed in the thriving black markets of the period, nearly all legally sold commercial goods were tied up by some manner of regulation or control.
Gordon S. Wood talks about some of this stuff in The Radicalism of the American Revolution, but I'll try to think of a more focused source in the morning.