The "4 I's" of Service Marketing

The "4 I's" of service marketing differentiate the challenges of marketing services compared to products. What are they?

1. Intangibility. Services are intangible, unlike products. They cannot be touched and sometimes cannot be seen. Largely, before purchased, services are based on an assumption or a promise of customer satisfaction. For example, purchasing a massage assumes or promises that the customer will feel better after receiving the service.
2. Inconsistency. Services are usually provided by people, and people are inconsistent among themselves in providing a service and sometimes personally inconsistent in providing services to the customer. For example, a haircut can be good on one visit to the stylist and not as good on another visit.
3. Inseparability. You cannot separate the service from the provider of the service. Services are  usually performed by service providers, so if there is no provider, there is no service. Services are sometimes provided by machines, such as a vending machine or an ATM. If the machine does not function, there is no service.
4. Inventory. Services cannot be kept in inventory like products can. So idle production capacity may exist if a firm pays for service providers but there are few customers. A doctor's office will staff its employees based on patients' appointments and perhaps walk-in patients. If patients cancel or do not show up, the practice has idle capacity that cannot be saved or inventoried. Furthermore, an empty seat on an airplane flight cannot be saved or inventoried for another time. It is a loss that cannot be inventoried.