Final answer:
A statement from a happy customer expressing satisfaction with a service or product is known as a testimonial. It is a positive endorsement that illustrates a customer's satisfaction through their positive experiences and personal evidence.
Step-by-step explanation:
The term that means "a statement from a happy customer, explaining exactly why he or she is pleased with the work you did" is a testimonial. Unlike a review or feedback, which can be either positive or negative and provide general impressions, a testimonial is specifically a positive endorsement that reflects a customer's satisfaction based on their experiences. For example, after enjoying a new hiking trail, a customer may provide a testimonial detailing the beauty and ease of the trail, thus recommending it to future hikers. Similarly, a testimonial for an auto mechanic would detail the quality of service and customer experience that made the customer pleased.
Such testimonials are influential because they use personal experience as evidence to support a positive judgment of the product or service. They can have a substantial impact as prospective customers, facing an array of choices, often base their decisions on the experiences of others as reported in testimonials.