Just Saying 'NO'

When is it in my best interests to say 'No' to a project?

When I'm undermined by someone in an organization who feels their toes are stepped on and so they attempt to belittle me by intentionally talking over my head about things outside the scope of my job?

I DON'T know everything and will gladly admit to it. However, I don't see the need to erode someone else's confidence and self-esteem when talking about web stuff with people who don't understand it. So do I need to put up with it from someone in a client's organization?

This one is a challenge for me because I was hired by the decision-maker to do a job, and being a tenacious woman, I'm inclined to do whatever it takes to fulfill what I see as my obligations to that client. But maybe I'd be better off firing this one...sure would save me some frustration.

BTW - may I always have patience and respect when I speak to clients about those parts of my job that they don't understand. And may I be struck down by a meteor if I ever intentionally try to erode someone else's self-worth.

Maybe it's just a toughening process and I need to be more self-assured.

I'd love to hear from other designers/developers and get some prospective on this....