Which term describes a seller's statement that guarantees the quality or functionality of a product?

The term that describes a seller's statement that guarantees the quality or functionality of a product is "express warranties." Express warranties are explicit assurances made by the seller regarding the characteristics, quality, or capabilities of a product. These warranties can be communicated verbally or in writing and are clearly stated as part of the transaction.

For instance, a seller might claim that a car will reach a specific fuel efficiency or that an appliance has a certain lifespan—these explicit promises create an express warranty. Such statements are legally binding, and if the product fails to meet the assurances, the buyer may have recourse through warranty claims.

Implied warranties, on the other hand, refer to unspoken or unwritten guarantees that arise from the nature of a transaction, rather than from explicit statements. Performance warranties could be considered a more generalized term, but it does not specifically address the seller's guaranteed statements about quality. Written warranties are one form of express warranty, but the key characteristic of express warranties is that they encompass both verbal and written assurances.