While I generally do not trust information from "advertisements", in this case I don't see how this is any worse than including a list of sources in the bibliography. What this could be is an attempt to use those other books to sell the author's through some reflected glory (or SEO-fu) but in that case, the author is still incentivized to recommend good books.

If this was a pure advertising piece, I might agree. In this case, it's more "hey I wrote a book on this, these are other books that are great". That's kinda different at least in my mind.

You mean you've _never_ bought a book for its bibliography?