Book publishing options are no longer a black and white decision but an array of grays
Book publishing, however, does not exist as two sides of a coin, with traditional publishing (often called royalty publishing) on one side and self-publishing (once disparaged as vanity publishing) on the other.
Instead, book-publishing options exist on a continuum. At one end are the major presses who carefully screen, edit, produce, and promote books, much as they have done for years. At the other end are the do-anything-for-a-buck outfits who will print any book, for anyone willing to pay their fees, regardless of its content, quality, or marketability.
In between them lies a vast array of options, from indie presses, to assisted publishing, to outsourcers, to any number of companies with intriguing labels, seeking to find a niche and fill a need. Although a few of these presses care nothing of books and only about money, most possess a sincere desire to help writers become published authors, advancing the cause of book publishing in the process (as well as earning a profit). They just do it in different ways.
These permutations of publishers are too numerous and evolving to delineate with any accuracy. An author should carefully vet each publisher before making a selection.
The key in evaluating them is to realize that each has a business plan and must make money. Comprehending what their plan is (sometimes we needs to dig a bit) and understanding how they make money (even nonprofits must generate income) will provide a basis for determining if their sweet spot matches a writer’s needs.
Book publishing exists on a continuum, as do the needs of the authors they serve. Finding the right match of publisher and author is essential for the success of both.