[katzgrau]

If the client is coming back with clearly unscoped changes, it's generally out of the question. Be polite at first and let them know that it's "out of scope" and that you could estimate the time required to do it.

When I said "clearly over budget," I meant in terms of your own estimate. Sometimes feature X takes longer to build out, and there's the inclination to cut corners to get things done so you don't drive your effective hourly/day rate down, assuming that the poor estimate was yours and you'll eat the cost.

But expanding on that, do quality work regardless of the scenario, such as:

* The codebase is already a pile of s* left behind by someone else * They're miserable, complaining, sons a' biches no matter what you do for them A fix could be sloppy and take 1 line of code, or quality and take 10

That kinda stuff.