Do you need an ISBN number to sell your book? This question comes up constantly. The answer is, unfortunately, it depends. An ISBN number is a unique number, attached to a barcode, assigned to a book that identifies it for SKU systems for inventory tracking. If you want your book to be sold “wide” meaning that it’s available everywhere, you might need one. Maybe. If you just want to sell your book on Amazon, they will provide a unique ISBN that only works on Amazon, and they won’t charge you anything for it. If you want to sell your book…