Did they claim to be the author of the book? If so I would say verification would be warranted in that situation. At least something that proves the name they wrote the book under ( remember many writers use pen names, as an example JK Rowling uses a male Pen name as well )
If the content was used as additional information which is placed in quotes (probably should be sourced) than verification would be out of line.
My opinions of course.
Nope - from what I saw, basically the whole post was content from a book verbatim. The poster did not use quotes or mention a source. The commenter pasted a picture of the content from the book and asked for verification.
I see @steemcleaners has commented in the post so it's on the radar now.