Final answer:
The degree of tangibility has the greatest impact on the ability to define, measure, and control service quality because it determines how quantifiable a service is, and quality of intangible services is often subjective.
Step-by-step explanation:
The characteristic of a service that has the greatest impact on the ability to define, measure and control service quality is the degree of tangibility. Tangibility refers to how easily a service can be quantified and measured. With intangible services, quality may be largely subjective and based on personal perceptions, which can be influenced by various intangible aspects.
These aspects include satisfaction guarantees, the brand's reputation for high quality, and additional services offered like free delivery or a loan for a purchase. Advertising can significantly shape these perceptions, leading to strong brand preferences that might not align with any discernible difference in the actual product or service. This influence highlights the challenge in defining and controlling the quality of a service.