If I don't have a particular skill set and the client wants me to "do the best you can," my price goes way up and I tell the client why. If I'm going to have to pay someone to fix up a mess I made I have to be able to afford it.
After I questioned this policy, he confirmed that the higher rate is by the hour, not by the job. His rationale, it seems, is to create price resistance against clients pushing work on him that is beyond his abilities -- and to cover his costs of subcontracting it out if they succeed in putting him in over his head.
There may be some merit to this from the client's perspective, too. If the work lies outside the consultant's experience, it could simply be more difficult or esoteric material, which would mean that its production creates a higher value than other more common tasks.
On the other hand, this could also represent a gap in the skill set of the consultant. In that case, the client isn't receiving the same value for the work performed as when the consultant is operating within his/her technical comfort zone.
I've always tried to base my rates on the value provided to the client. I've been known to reduce my rate when I'm learning a lot of new technologies, because some of that time represents value to me in the form of education.
As Earl Nightingale always used to say, the money you receive will be in direct proportion to the service you provide. I might insert the word "perceived" right before "service," but the principle still holds. Clients will continue to pay what they think your services are worth, and no more. So it seems counterintuitive to me that you would charge more for work that you can't perform as well. Unless, of course, the intent is to drive away that business.
How about you?
Chip Camden has been programming since 1978, and he's still not done. An independent consultant since 1991, Chip specializes in software development tools, languages, and migration to new technology. Besides writing for TechRepublic's IT Consultant blog, he also contributes to [Geeks Are Sexy] Technology News and his two personal blogs, Chip's Quips and Chip's Tips for Developers.