Yog's Law, formulated by SF and Fantasy author James D. Macdonald, is a basic principle that all writers need to keep firmly in mind:

That's it. Money flows toward the writer.

There are various companies, individuals, Web sites, and service providers who will try to divert money toward them. Don't make it easy for them. The only place a writer should sign a check is on the back (as James Macdonald has also said). Writers write books, agents promote and submit them, and, if they are successful, receive a commission on a sale. Publishers have editors who edit, and are paid a salary by the publishers, who, in turn, pay writers an advance and royalties, and they distribute and market the book.

• Writers don't pay publishers to be published. Commercial mass market, text, and trade publishers don't sell their books to writers. They have a sales staff. You can find their books in your local stores and libraries.
• Writers don't pay agents or editors to read their manuscripts. If there's a fee involved, other than the customary commission on a sale, be very cautious.
• Writers don't pay editors at publishers to edit their manuscript. If a publisher suggests that you hire or pay one of the publisher's editors a fee, be cautious. Editing, proofreading, typesetting, book design, distribution and cover art are part of the standard services publishers provide. They don't charge. If you need a professional independent editor, be choosy.
• Writers are not generally expected to market or provide or pay for ancillary services. Be cautious about using literary service providers.