The Kindle book "Sign Language for Everyone: A Basic Course in Communication with the Deaf" has an unusual font (as pointed out by rflashman
here).
I enclose screenshots of this publication and also HarryT's
Dickens, Charles: A Tale of Two Cities (Illustrated). v2, 24 Dec 2007. The latter as an example of the standard font (Caecilia). These are on the 4th font size, to make the fonts easy to see. These are actual dumps of the screen, using Alt-Shift-G see
Hacking the Kindle part 3: root shell and runtime system.
Nelson Books are forcing left justification (usually considered bad practice, because it removes user choice), but they also have a different font from usual and a narrower line spacing. The lowercase e and g are particularly different in the two fonts. It is possible to specify a specific font in the MobiPocket format, but you have to know its exact name and I'm not sure how to force line spacing within a MobiPocket e-book. If the book was DRM-free then it would be easy to see how this is done, but as it is I am in the dark.