Interesting and informative article.
Nothing cries amateur so loudly as a book riddled with spelling and typographical errors, which is unfortunately typical of mill-published and self-published books.
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If you try to copy edit your own book, you will fail. Once you get the look of the words stuck in your head, often errors will become invisible to you. You simply must subject your book to outside editing, if you wish to publish a product that you can be proud of and that other people take seriously.