Situation 1: When there is an actual problem, then is customer right in approaching the service provider for a solution?
When there is an actual problem with the product or the service and the customer approaches the service provider for a solution, then the service provider should ensure that the problem is solved as soon as possible with minimum botheration to the customer.
For example, there is genuine problem with the laptop of a customer and he lodges a complaint with the service provider, then the service provider should check and rectify it so as to satisfy the customer's demand.
Taking another example, if a person visits a restaurant to have dinner and finds that all the waiters instead of taking orders from the customers and delivering them, are just talking to each other and, thus, the customers have to wait for long before they are served. So if that person complaint about this to the service provider then the service provider should immediately take an action to rectify this problem so as to satisfy all his customers.
Now by solving the problem with the product/service, the service provider can also become right.

Read this interesting article at..
http://www.coolavenues.com/know/mktg/shashank-customer-1.php

Actually, customer concerns and/or complaints are the business owner's best tools for growth and improvement... no matter what the scenario may be.

However, sometimes people complain just to get something "extra" out of a business relationship. This is the wrong way to go about it, since in any good business transaction, both parties should feel that they win.

Those customers do exist though.