Whether you're a partner at public accounting firm, freelance graphic designer, or account executive at a printing company, chances are that if you have been employed at any point in your life, you have spent some time interfacing with your's or your employer's clients.  As someone who has worked in client-facing positions for over 10 years, I have definitely have a great deal of experience in dealing with clients myself.  And I have definitely had my share of the good and the bad ones.  But do you really have to take the good with the bad?  Depends.  Here are my top 3 non-negotiables:

  1. Verbally abusive and aggressive.  This includes yelling, screaming, belittling, and putting people down, etc etc etc.  Aggressive body language (i.e., raising arms) is also never, ever acceptable behavior.  Solution: the next time it happens, break it off immediately.  Inform them you won't take their abuse anymore and would like to sever the relationship.  When you are terminating a relationship mid-project, state that you will send their final invoice and work to-date the following day.
  2. Payment issues. This includes non-payment, late payments, and constantly questioning charges. Obviously, the whole point of doing the work is to make the money.  Solution: establish tight payment schedules.  If that doesn't work, take them to collections.
  3. Always trying to get more work for free.  These are the ones who are given an inch and will always try to take a mile.  They don't respect your time and are usually dissatisfied with your work and create a constant back-and-forth cycle.  Solution: include specific terms in your contract, specifying items such as the number of concept and revision rounds.  Also specify your hourly rate for out-of-scope work.  Then, make sure all the time you spend is reflected in your invoices.

And in this job market, people are hungrier and more desperate than ever to land that next client/job.  As such, it's more difficult than ever to turn down work and be selective, only taking on those clients who are right for you and your business.  Let's face it though, the most difficult clients, usually aren't the most profitable.  So when you are declining new work solicitations from a past client, you can take one of two routes. 1) Be direct. Let them know the reasoning behind your decision to turn down the job.  2) Use a non-confrontational approach. Tell them you do not have any availability in your workload right now and refer them to a competitor.  Just don't lie; you definitely don't want this to come back to you.  Try to end the relationship on the best terms possible, given the situation.

In the end, by accepting unacceptable behavior once, you are setting a precendent.  You teach people how to treat you.  Overall, consider the client's history and if you still don't feel it's worth it to keep the relationship, then don't!