We go to a lot of trouble to make our book descriptions as good as we can — not just their content, but the way they look. Many of us have learned basic HTML tagging in order to provide formatting for book descriptions as part of our work publishing a book.
As soon as you go beyond the world of Amazon-only, you begin to lose control of what distributors and retailers do to your pretty book descriptions. And it takes special effort to make the book description inside your book look good, too.
Doesn't always work, though. Not all methods are suitable for all situations, and there are limits to what you can control.
As in all such things, the devil's in the details.
(click on any image below to enlarge it)
HTML Markup to use for websites
What I think of as the original text usually appears on the book's product page on your own author and/or publisher websites.
You have complete control over what this looks like.
You can see a simple use of <strong> and </strong> to mark the bold section (same as using <b> and </b>). This was created in WordPress, and the paragraph behavior is instantiated by the underlying WordPress theme (in other words, I didn't need to place paragraph marks <p> and </p> around each paragraph.)
HTML Markup to use for ebook front-of-book blurbs
Ebooks are special packages of HTML files, in a compressed (zip) container. I make my ebooks using Sigil, and each chapter is an underlying file in the container. The opening page shows a book description.
You have complete control over what this looks like, within the limitations of HTML supported by ebooks.