This popped up at the Passive Voice the other day: https://booklife.com/create/art-design/06/28/2015/top-five-diy-book-layout-mistakes.html
Do your books look like books? No, not as in they have cover, pages, copyright info, table of contents, but if you borrowed someone else’s e-reader and compared your book to a Big 5 or small press book, does yours scream “Hi, I’m a bad Word to HTML conversion?”
If so, you might consider re-working the file and re-uploading it. We indie writers are trying to sell to people who also read print books, and Big Publisher books, and we need to look as good as those do.
Some of the article’s tips lean toward print rather than e-book, because readers are going to select font, font size, and other things that can affect pagination. But others had me stop, blink, and say, “Ah, yes, that’s a good point,” especially after I pulled a few print titles off my shelves and glanced through them.
Having a program like Vellum or Jutoh does make a lot of the e-book formatting much easier, but I have caught a few rough spots in for-print formatting. And there are more tutorials and guides appearing for using Word, Caliber, Scrivner, and other word-processors to set things up so that when you convert to EPUB, MOBI, or PDF, your files come through safe, sound, and good-looking.
Ideally, the story in the book is so good that readers will forgive or miss completely awkward margins, wandering page numbers, and the occasional header in strange places. But if you are hand-selling a book, and someone flips through the copy, the book needs to look familiar. It has to mimic a professionally formatted title. I know, because I’ve picked up indie books, thumbed through, winced, and put them right back down, not even reading the first page, because the formatting was so poor.