Hi Patt,
I suddenly got a flashback for myself after reading your problem with your client. I guess everyone's had their share of runs with "picky people". I'm confident you're good in what you're doing, and that's not where the issue lies.
The real problem is with our clients, who wants a final say to things. I had two recent comissions, and both of them did that on me! And guess what, both of them had me to "make that little 'perfect adjustment'" (the earlier commission had me travel all the way down to the gallery in a cab, in my crutches!)
The thing is, i didn't do anything (though i didn't say that to my clients and not even to my gallery owner), just a little action on the canvas/ drawing. And they tell me "THAT'S IT!!"
The very fact is that they want you to make the correction THE WAY THEY WANT IT, PRONTO. And i realised these people tend to be either power-people or control freaks. So don't let them bog you down because of what they say. Emotionally take a step outside and be professional. If they want you to 'conjure up the magic', then wave that brush, maestro!
Give them the 'rush feeling' of being in control of you - for once in their lives.