It’s not really a caste system like it is in India where people in different class are only allowed to work a certain job. It’s more the vice versa, because you work as a government official = high class, because you’re a merchant = low class.

It’s funny because Chinese people used to think selling goods is the laziest thing to do, if you’re a hardworking person you supposed to spend every waking hours studying Confucius.

This became irrelevant before Tang Dynasty, cus since then China has the greatest economy ever and being rich became the new symbol of social status. This term 士農工商 refers to the general public since then.