Oh my, this is actually a complicated question with lots of replies based on so many factors, but OVERALL, The whole complaint issue can be resolved ahead of time by YOU being (or learning to be) the one in control

Working on commission means you are an artist for hire. Plain and simple.

The other determining factor in your “complaint meter” is PRICE.  Price determines everything.

With over twenty years and thousands of portraits behind me,  I find that the more money  people invest in my portraits, the more cooperative they are. Seriously. The $300.00 person will, without exception, ask for more changes than the client who just invested $5,000.!

But there’s much more…..although staying in control means you are the expert and the professional, you need to be skilled enough to be able to do what you have been hired to do! You are, after all, working for them

I have found many artists who never practice their craft until they get a commission and then wonder why the client is unhappy.
Your client should not be your guinea pig
Many artists I know, give painting workshops and the next thing they know their happy students are getting a commission (good) but the instructor is getting phone calls and emails from that student wanting to know why their new client is not happy with the results (bad) …the photo is not clear, the eyes are in shadow, etc., etc………..If you are skilled enough and have painted enough, and know what your subject really looks like,  then you know how to work around bad photography.

You are confident of your abilities  because you have practiced!  And along with that comes your PEOPLE skills.

Browse the articles on my other site, www.artcareerexperts.com and find the one about how to stop clients from coming back for changes AFTER the sale. It took me investing a lot of money into non-art marketing information to discover THAT sales technique (I had to learn it too)
In summary and fact, (and I stress this in my ebook- )  clients do respect your professional opinion and expertise  more if you “charge” enough money for your work! They put more value in your opinion as the expert. “price determines everything.”

Theresa
The Portraits: www.MTheresaBrown.com
The Artist’s Day: www.mtheresabrown.blogspot.com
Art Classes: www.ArtStudentAcademy.com
Career Artists: www.ArtCareerExperts.com

Steve just delivered my portrait to our client in Virginia. He hung the 30 x 40 oil high above her shelving unit (moved out to accomplish this) to hang side by side with a portrait I created of her 5 years ago. We had no problem  offering to help her with this task even though she had not asked us.  Over the years she had invested not only her money but her trust in our abilities and we rank our clients among our friends and acquaintances!

When we create art for a client, we offer everything from recommendations for the framing to delivering it and to installing it!  Simple courtesy goes a long way in customer/client loyalty!   And every business that sells anything to the public knows this and makes every effort to make sure their client is satisfied with every aspect of the sale!  Artists have a tendency to think that clients owe them when it is, in fact, it is the other way around!  Don’t confuse today’s art client with art clients from the past who were taken in (with the help from art galleries and their agents) with the arrogance and actions of a few of the artists of the twentieth century. Today’s consumer is savvy, knowledgeable and rarely needs her hand held. Unlike her teenager, she does not need to put up with an artist with an attitude!

So do you, your art and your reputation a favor and add a little customer service in with your art sale. Courtesy goes a very long way!  And don’t worry, the teens eventually figure this out!

All done and loving it!