Final answer:
Adam Smith describes a successful interaction between a buyer and a seller by introducing the concept of the 'invisible hand', which refers to the self-interested behavior of individuals in a market system leading to positive social outcomes.
Step-by-step explanation:
Adam Smith, in his book The Wealth of Nations, describes a successful interaction between a buyer and a seller by introducing the concept of the 'invisible hand'. According to Smith, when buyers are looking for the best deals and businesses are motivated to provide goods and services that meet consumer needs, a market economy functions efficiently. The 'invisible hand' refers to the self-interested behavior of individuals in a market system leading to positive social outcomes, such as economic growth and improved standards of living.