Finally, to speak honestly, reselling for profit isn't "unprofessional work"; the essence of business is value circulation and matching.

You deliver the right products to people in need, solving the buyer's demand and helping the seller sell their goods, and the profit you make from the price difference is the reward for matching supply and demand.
For ordinary people starting a business, the easiest way to get started is to run through this smallest closed loop.
Seeing supply and demand clearly, calculating costs and profits in your mind, acting quickly to execute, and controlling risks well. Business will naturally grow bigger and bigger.