There’s a blurb underneath the title linking to third party page. This page is selling a really quacky looking book, that has no obvious connection to the autho

There’s a blurb underneath the title linking to third party page. This page is selling a really quacky looking book, that has no obvious connection to the author of this article. Is this an ad? It doesn’t look like normal ad placement. It looks like the author of the article is promoting it. And it seems really quacky. I wish substack was clearer on whether this product is endorsed by the author of the article.