(1) A sale in which the quality of goods is determined based on samples refers to a sale in which both parties agree to use samples as the quality basis for the transaction. In such a sale, in accordance with Article 5 of the United Nations Convention on Contracts for the International Sale of Goods, the quality of the goods should be the same as the sample or pattern of the goods provided by the seller to the buyer. Otherwise, it shall be regarded as inconsistent with the contract, and the seller shall bear the liability for such non-conformity. Since most sales based on samples are goods whose quality is difficult to standardize or standardize, it is sometimes difficult to ensure that the quality of the goods is exactly the same as that of the sample. Therefore, there are also situations where the contract stipulates that the delivery quality should roughly match the sample. (2) The sale and purchase of goods based on specifications, grades or standards to determine the quality of goods. Specifications refer to some main indicators that reflect the quality of goods, such as weight, length, size, purity, strength, tensile strength, etc. Grade refers to the level classification of similar products, such as first grade, second grade, special grade, etc. Standards are the standardization of specifications and grades of certain types of goods by enterprises, industries, governments or international organizations. When conducting such sales of certain quality, the goods delivered by the seller should be consistent with the specifications, grades or standards specified in the contract, otherwise, it will be a breach of contract. (3) The sale and purchase of goods based on trademarks or brand names to determine the quality of goods. In international trade, for certain goods with stable quality and established good reputation, the quality of the goods can be determined by trademark or brand name. Generally speaking, a trademark or brand name, especially a reputable trademark or brand name, represents a certain standard of product quality. Therefore, such transactions do not need to specify specific standards or provide samples. However, since products with the same trademark or brand name may be produced in different countries, there will also be differences in specifications. Therefore, some sales based on trademarks or brand names will not only stipulate the brand name or trademark of the goods, but also have certain requirements on the product. Specific specifications are specified. (4) Sales and purchases in which the quality of the goods is determined based on instructions. Product instructions are written materials that describe the performance, structure, etc. of the product. In international trade, when buying and selling some equipment with complex structure and performance, detailed instructions are sometimes required to specify its structure, materials, performance and usage, etc. In sales based on instructions, some contracts, in addition to the instructions, also stipulate quality assurance clauses to ensure that the quality of the goods sold by the seller meets the technical indicators in the instructions within a certain period. If the buyer discovers that the quality is inconsistent with the instructions during the warranty period, If the instructions do not match, you can request a return. The quality terms of the goods must be clear and should be performed in accordance with the quality agreed in the contract. Sometimes exceeding the standards agreed in the contract will cause disputes, especially when the buyer has special requirements for the goods. For example, a hair dryer ordered by a customer does not require Very long life, which is conducive to market replacement and reduces costs.