[ghaff]

I don't have a lot of experience with software services but when I was a consultant (IT industry analyst), most of the work that we did was fixed price. Sometimes this was straightforward because the time was explicitly capped (e.g. an advisory day). Other times, it was a standard deliverable of a type we had done many times before (e.g. a paper); these could take more or less time in a given case but they were pretty predictable. And sometimes, it wasn't all that standard but we knew the day rate we were aiming for and could take a pretty good swag at the time required; here is was very important to spend time up front scoping the work.

(And sometimes, we really weren't sure, in which case we wouldn't do the job for a fixed fee.)