My promises to you:
If you decide along the way that you do not like the way we work together, be sure to let me know so we can discuss changes in the way your project is being handled. If you continue to be unhappy after we make adjustments, bring your continued disatisfaction to my attention. If we cannot make adequate and appropriate arrangements, either of us may agree to sever the working arrangement at any time. You will be responsible for paying only for the work you wish to use.
If we agree to a project-based work arrangement, you have two additional guarantees.
First, since you and I will have worked together to determine a schedule, I guarantee that your final deadline will be met or you will be expected to pay only half of the quoted price.
Second, I guarantee that the maximum estimated price quote we agree to at the beginning of the project is, indeed, the maximum amount you will be responsible for paying; under no ordinary circumstance will that maximum be exceeded.
You do need to keep in mind, however, that any change made to the project once we begin work may mean changes in timetables and prices. No change should come as a surprise to either of us, though—I will discuss obstacles and problems with you as they arise just as I expect you to discuss conflicts and surprises with me.