Work terms for projects such as e-books, blogs and articles vary. If I know and have worked with someone I am open to payment after the project is complete. If I don't know, or haven't worked with the person then I will request Guru's Safepay, or prepayment for the project. Establishing a relationship is important.
This is the standard in the industry so both clients and writers can safely approximate the size of a project if not using word count. However, for a writer, word count is the most important determination of project size.