How can vanity publishers and self-publishers be distinguished from one another? And why is it important that we make this distinction?
When an author self-publishes then the copyright page of his book bears the name of his imprint; his publishing company—even if it publishes just one title—owns his ISBN and the publication rights to that book. As publisher he’ll know exactly how many copies of his book have been printed, where and when they have been sold, and who to. Consequently he remains in full control of both the production and distribution of his own books.
A vanity publisher, however, will usually have its imprint listed on the copyright page of each book it publishes, and will control most aspects of their production and printing; consequently, the author will not have authority in the publication of his own book, nor will he have immediate access to vital information about stock levels and sales records. While vanity publishers often masquerade as mainstream or self-publishing services, their books usually carry the name of their own imprint: and by definition, if the imprint doesn’t belong to the author, it’s impossible for them to have self-published the book.
If you're considering self-publishing your book then it's important that you understand this: otherwise you could end up making a very costly mistake, and losing your precious first rights to an unscrupulous vanity publisher.