Learning to say no is widely covered in our profession. It is a skill many of us have to work on. It took me a long time to identify my limits and realize that yes can be a huge and attractive trap. There is another aspect of our profession that does not receive as much attention: learning to hear no and respond properly.
Not too long ago I was contacted by a law firm. They seemed to be in a big hurry to replace their previous translator. They invited me to come to their offices for a meeting and I promptly agreed. Error #1.