Guesstimate.

One of the things that scrolls my nurd is when clients ask for time estimates for editorial work. Not the deadline; they mean how many paid-by-the-hour hours will it take. 

I understand that they have their own paperwork to file, and that the bean counters think that estimating time to copyedit or proof a book ought to be as straightforward as estimating time for a delivery of rocks. But it doesn't work that way.

Actually, the proofreading is not too difficult to estimate, since by doing a couple of pages quickly I can figure out how long and messy the job will be. Copyediting is a little harder, since it involves editing for sense and continuity, which can be an issue if the book turns out to be complicated. Estimating for fact-checking is the worst, though, because it's hard to tell right away if the author is a know-nothing dumdum who is going to ensnarl me in a world of irritation. 

The estimate I'd like to send

You can give a book a quick going-over, but that won't tell you if the author is using half-baked or completely unbaked sources, is mistranslating foreign words, is making wild suppositions hidden by passive language, or a hundred other things that make a book a pillar of lies. As a fact-checker it is not enough to say "WRONG!" like Dom DeLuise in Blazing Saddles, although it would be satisfying. I'm expected to provide the right information, or exhaust all efforts to find it. 

The problem is, unlike your plumber who discovers hidden problems, I have little recourse when an estimate is entered. One large company in particular makes it very hard for everyone if a job comes in over estimate, and it delays payment by weeks or even months. They make strong incentives to get me to provide on-target estimates, even though there's no certain way to do it. Either I overestimate and get a rep as an over-charger, or I underestimate and wind up working free hours. 

Anyhoo, it's made me more sympathetic to the contractor who finds unexpected issues like asbestos or bad wiring or unknown leaks or any of a number of things unexpected in a renovation. Sometimes you just can't tell where the big problems are hiding, in homes as in books.