For the past 700-something newsletters we've shared, I have tried to focus on who your customer is.

Today I'd like to talk about something even more important — who your customer isn't.

In David Mamet's Glengarry Glen Ross, people who are not your clients are described simply as folks who, “…just like to talk to salesmen.”

One of my star clients has internalized this lesson. My student has a high touch, long-term relationship with his own clients. He only works with a few clients each year and speaks to them every week. I have taught him how to explain the value of his professional services; I have taught him how to “get off the phone” without giving away the store.  I have taught him how to “strike while the iron is hot.” I have taught him how to get paid for his expertise rather than his time.

Recently he added to that list when he explained how he has absorbed another crucial lesson: determining who he “…cannot, should not, will not try to help.”

Here is a summary of our conversation:

“Mrs. Williams talked for fifteen straight minutes about how her business was different from all the other businesses with whom I had worked these past 40 years. Hearing that, I decided to add my usual toxic individual up charge by raising my price 20%.

Then she went on to speak without taking a breath for another ten minutes about how difficult her ex-husband was, how most of the problems with their business were a result of his insensitivity, and how she never should have gone into business (or marriage) with him in the first place.

At that point I decided to charge her a 40% premium because she wasn't letting me get a word in edgewise and I wasn't sure I would be ever even get the chance to help her.

She then continued to speak for another ten uninterrupted minutes about how she had spoken to many of my colleagues over the years, how they were all charlatans, how they all just wanted to rip her off. But she explained how she knew that because of my standing in the community I would be able to help her even though those other professionals had not.

Rather than charge her my standard,  “you are trashing the reputation of folks whom I know to be competent and you'll be saying bad things about me within a few months as well” fee of an additional 50%, I interrupted her diatribe and said simply,  ‘I'm sorry, I cannot help you.'

‘But I am ready to give you my credit card along with my permission to bill your exorbitant $50,000 fee' she said.

‘No, thank you,' I replied.  ‘I'm sorry but I can't help you. Good-bye.'

You see, having a bad client is a nightmare from which there is no awakening. An account that contributes five percent of your income–no matter how much you assess your pain in the neck fee—but takes up 50% of your time and 80% of your emotional well-being is not a bargain.”

Interactions with clients never get better than the first time you speak to them. Not ever. The first conversation is invariably the best conversation you'll ever have and the downhill can be steep from there. Leopards will be wearing purple polka dots before this client changes her view that her business is different, that her business requires special attention, and that the world should stop spinning so that we can all attend to her every whim.

Yes, we all want revenue. Yes, we provide the best professional goods or services that we know how. And yes, we do the best we can to set proper boundaries.

But knowing which one client to avoid is just as important as attracting ten other clients whom you can help.

Maybe even more important.