Mari Ann, it does make a difference when you are very specific versus just saying, “I’ll do a developmental edit on this ms for $X,” doesn’t it? I’m also much more upfront about how much additional tasks cost than I used to be.
In the past I would sometimes add things on (“sure, I’ll review your query letter”) because they weren’t that much more time-consuming and “deliver more than the client expects!” etc. But over the years I learned that people actually value my services much more if I charge for them. And I’m also able to schedule my time more effectively if I’m not letting a task become bigger than agreed to.
Much of the time I find that people either expect to pay for the additional task or simply didn’t realize they were asking for something that wasn’t just a marginal “yeah, I can throw in the paperclip holding those papers together.”