Final answer:
The primary characteristic among the four unique service characteristics distinguishing goods from services is Intangibility. It is the basis for the other service characteristics: Inseparability, Perishability, and Heterogeneity, and significantly impacts product differentiation through aspects like guarantees, reputation, and brand loyalty.
Step-by-step explanation:
Among the four unique service characteristics that distinguish goods from services, the characteristic that is the primary source of the other three is Intangibility. Intangibility means that services cannot be touched, seen, tasted, felt, or measured in the same way physical goods can. This intangible nature leads to three other characteristics of services: Inseparability, which indicates that services are produced and consumed at the same time; Perishability, meaning services cannot be stored for later use or sale; and Heterogeneity, which refers to the variability in the quality of services.
Intangible aspects like guarantees, reputation for high quality, and brand preferences shaped through advertising play a significant role in product differentiation. These aspects can create a distinct perception in the minds of consumers, who may have strong brand loyalty even without a discernible difference in the product's physical attributes.