I did a bit of research for this article, after it occurred to me that I really wasn't sure how to answer this objection. How DO you know when the project is done?
Most clients will want to specify the items I gave up front: time, scope, and cost. But specifying all three variables will, almost invariably, lead to overruns, bugs, and dissatisfied customers. Why? Because software is inherently an abstraction. If I want to build a skyscraper, I can get an architect, draw some pictures, do a 3D model. I'll have a pretty good idea of what the concrete implementation of the skyscraper will be before the first shovelful of dirt is ever turned over. But software doesn't work that way. By the time you've put together a decent picture of what the software will look like, you're well on the way down the road and have probably put a pretty nice chunk of change into it. Now, you can try specifying time/scope/cost, maybe even do a good job of implementing it. But chances are if you've done that, you've told the clients you can't make that little change they wanted without changing the contract, updating the design, and of course, charging a lot more money. Now everyone's unhappy. The clients didn't get the change they wanted, so they're not as excited about your product. You're unhappy - or you should be - because you have an unhappy customer and a product that isn't as good as it could be.
So here's the solution: Rather than allowing quality to be the dependent variable, hold it constant and let another variable, say scope, be dependent instead. So now, you've got a contract that says you will work on this project for x number of months, and it will cost y dollars per month, and for that money, the client can choose whatever features they want next at the end of the month. Or, to put it another way, get rid of the deadline.
Whew, I think I'm either going to have to stop this series, or write a book. Next time, I'll finally come back to my church application.