hi david,
I'm working in printing house



>
> A sad story: My context-typeset dissertation was printed/distributed by a
> POD publisher with aweful typographical errors (like all commas in the main
> font being replaced by an ff ligature).
>
Horrors, and really strange


> Obviously the printer didn't check their results.
>


The file *reads* fine both for me and the publisher, but the printer let us
> know that the file is unprintable due to problems with fonts not being
> embedded
>
This is  a common problem


> (why they originally printed an "unprintable" file I'll never know).
>
money ?


>
> Now as far as I can tell, fonts *are *embedded. It was made with context
> MKII, using hz and hanging punctuation, etc. When I look at the document in
> Adobe Acrobat, and check the document/font details, it gives a list of
> embedded fonts only.
>
Are you sure?
As pable write
pdffonts is very good

>
> I'm not certain that the printer is in the right, but how can I tell? Is it
> possible that the pdf was altered when transferred from me to the publisher
> then to the printer?
>
With very hight probability , no ; pdf is a 'bynary' format
an alteration will broken the file.



> That compression of the pdf (zip) had any impact?
>
With very hight probability , no .

> Any other possibilities? What do you need to know to offer advice?
>


> I can send the file or a part of it if it is needed.
>
yes, if you want .


-- 
luigi