Well, you want to be flexible and accommodating, but you want to cover yourself from scope creep and you don't want to set the precedent that they can change anything whenever they want. I would probably do small changes for free, but call them out as exceptions, like "Sure, I think we can slip this change in under the radar, without affecting the project timeline!"
tptacek posted a great line the other day which I stole for my personal use: "I am happy to do whatever you'd like and make whatever changes you'd like but I need to remind you that we have a fixed schedule for this project". This line concerns scheduling, but I think it could easily be adapted to deal with scope and changes.
Can you elaborate more on using that line? The purpose of using that as I read it is to say "Yes, I can attempt to implement that new/extra feature, but if I am unable to do so within the original project schedule, there will be an extra fee for my time." Is that the intent?
The original meaning was, "You call the shots, but if you add a bunch of changes, we're going to slip on the schedule."
What I meant was that you could probably use a similar line, to the effect of, "I'm happy to change this to do X instead of Y, but since that's a rather major change, I may need to send you a revised quote for the feature. Would you like me to do that, or maybe do Y', which should meet most of your needs for now?"
tptacek posted a great line the other day which I stole for my personal use: "I am happy to do whatever you'd like and make whatever changes you'd like but I need to remind you that we have a fixed schedule for this project". This line concerns scheduling, but I think it could easily be adapted to deal with scope and changes.