It is not illegal to earn price difference if the source of goods is regular. As long as there are no unfair and unreasonable trading conditions in the purchase and sale of goods, it is not illegal not to carry out compulsory trading. China's laws clearly stipulate that business operators who provide goods or services to consumers shall perform their obligations in accordance with this Law and other relevant laws and regulations. Where an agreement exists between a consumer and a business operator, obligations shall be carried out in accordance with that agreement. An agreement between the parties concerned shall not, however, be in contravention of laws and regulations. When providing goods or services to consumers, business operators shall abide by social ethics, conduct business in good faith, and protect the legitimate rights and interests of consumers.
 Legal basis
 Article 16 of the Law of the People's Republic of China on the Protection of the Rights and Interests of Consumers A business operator that provides a commodity or service to a consumer shall perform its obligations in accordance with this Law and other relevant laws and regulations. Where an agreement exists between a consumer and a business operator, obligations shall be carried out in accordance with that agreement. An agreement between the parties concerned shall not, however, be in contravention of laws and regulations. When providing goods or services to consumers, business operators shall abide by social ethics, conduct business in good faith, and protect the legitimate rights and interests of consumers; It is not allowed to set unfair and unreasonable trading conditions or force trading.