There are better ways to create goodwill. Exceeding expectations or being a fun person to collaborate with, for example. And neither of those approaches put your livelihood in jeopardy by introducing unnecessary risk with a gimmick.

I'm starting to feel like the 37signals guys in this thread. There's something to be said for making a living by doing good work and charging a fair price for it.

Goodwill works when dealing with clients in small companies who have margin to offer goodwill.

Start dealing with a BigCorp and there is no goodwill to be had. In fact, this pricing mechanism may backfire because the person you are doing the work for isn't the person who signs off on the budget.