The Customer reference article from the English Wikipedia on 24-Jul-2004
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Customer

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A customer is someone who purchases or rents something from an individual or organisation.

Types of Customer

Customers can be classified into two main groups; Internal and External customers. An internal customer is someone who works for the organisation, possibly in another department or another branch. External customers are essentially the general public.

These two groups can be further broken down:

Internal Customers

External Customers

Needs and Expectations

Customers have needs and expectations that need to be observed by the organisation. A need is something that the customer needs, like car insurance being low. An expectation is something that the customer won't necessarily get but they expect to get, like a car getting from a person's place of departure to their destination.