I also did some online research and questionnaires around what would make e/i-print books sell in terms of word size and over a 6-month period reviewed feedback which clearly suggested that for print books that people would buy off the shelves in bookstores, people were looking for more substantive books (128k plus) and would be paraded to pay £9.99+ for this, whereas as an e-mail people wanted, (neigh expected) smaller (28k approx.) e/i-books that they could easily read on their travels to and from work and get through over a few ways but were expecting to pay no more than about £4.99. Any other studies out there I would be interested to read.
My main point is that, (with the exception of big brand author brands, and I think they even struggle at times), replying solely on income of books during this clime and the way the books market is saturated, may not be entire viable and necessitate the thinking, ‘let’s not given up the day job’. However, thinking more laterally at others associated ways of monetorising with, in my case, advise, support, presentations, workshops, mentoring, amongst others things, `(with still promoting and marketing the books), affiliates & other services via the website(s) enhances the income streams that collectively make the while exercise give ROI.