I've heard other consultants advise "always under-promise and over-deliver." Is this a good approach?

This is logical if your goal is to avoid "under-delivering." However, "under-promising" might be a poor strategy to secure business and please your client, who is likely looking to do the absolute best possible with the available time and resources. A better approach might be to make a meaningful, realistic promise of delivery and then work very hard to absolutely deliver (or over-deliver) on that ambitious promise.

There are many ways to do this. You can single out one facet of the assignment on which you can make a strong commitment, perhaps even making your fee partially or totally contingent on its delivery. At a minimum, you should mutually review the risks and mitigation strategies you will both take to assure satisfactory delivery of your services so that the client gets the outcomes they expect.

Tip: Be very clear with the client what you plan to deliver and when. You are dancing close to an ethical line if you tell them one thing and plan to deliver something else (even if it is an improvement on the cost, quality or speed of your initial commitment). The ultimate risk of under-promising: it may be so unambitious that you may not get a chance to deliver it because you lost the job to another firm with more realistic and ambitious plans.

© 2010 Institute of Management Consultants USA