[Katsunami]

Before I put a book into my "Finished" library, I rip out all embedded fonts and @font and font-family references.

I've not yet looked at a pure AZW3, but after converting or extracting an EPUB, I've had no problems with block quotes or repeated line-height or font-family declarations. That could be the books though; I've not bought many from Amazon up until now.

What I meant was that I don't want to change a book anymore after it's "perfect"; which means, no custom fonts except where necessary for special characters, and no EPUB errors as much as possible.

I use a lot of EPUBs from the Kobo store, which I convert to AZW3 using Calibre, and they work perfectly. To be honest, I expect an EPUB from the Kobo store to work correctly on a Kobo device after having it converted/changed to KEPUB...