"It's not personal, it's business." Can't help seeing Tom Hanks and Meg Ryan in my head when I say, think or hear this.
So often we take things personally when it's not about us -- and when you're in a service firm, it's ALWAYS not about us. When people react to an email or request without context it can feel personal, and I do spend time reminding my very conscientious, very hard working staff that "it's not about you -- it's about what they have to deal with" or "they don't know what they're asking."
(Frankly as a side note, "they don't know what they're asking" is probably more prevalent, because everyone thinks they know what we do all day, but most have no frickin' clue what it takes to make our work happen....but that's another blog post.)
HOWEVER -- sometimes business is personal....let me refrain, sometimes the service firm business is personal.When personality and fit and ability to serve define how well you can get your job done - business becomes personal.
And the first rule of personal business needs to be courtesy, or it will collapse regardless of results. If you find yourself in a situation when you are not being extended the basic courtesies of business (they are: returning phone calls or emails in a timely manner, providing direction when giving feedback, being direct without being rude, being HONEST) that's when it crosses the line and it's time to GET OUT.
When business becomes personal it's time to change or get out of the game.