Back in early July, there was a brouhaha over Sprint's (NYSE: S) decision to terminate roughly 1,000 subscribers because of persistent calls to customer service (the average was about 40 to 50 calls per month).

But isn't the customer king?

Maybe so, but there are some customers that can wreak havoc on your business. For example, there always seems to be some people who pay late (or not at all). At the same time, they keep demanding more services and changes. Such customers can eat up lots of resources and drag down the performance of your business.

True, with some customers it might be smart to put up with their bad behavior, even if you must take a loss on their business. This can be the case when you want to land a marquee name. In this situation, a troublesome customer can be worth the price if they provide a boost to your credibility and a reference for future business.

But this is the exception. Basically, to run a profitable business, it's critical to be rigorous on the return on each customer. Simply put, there are some customers that are not worth it.