You mentioned: "many times clients have already done this work. Ask them for copies of their market research reports when you start a project. It will save you a ton of time and effort!" We do this with most of our clients, like you said we have found that around 75% of the have some kind of Market research done, that saves you a lot of time and helps setting up the right SEO Strategy.
I will give you a very simple example. Let’s say you build up an audience of 50,000 readers and out of that 50k you have about 1% that trust you (1% of people that trust you online is actually very huge), so that equates to 500 readers. Out of that 500 readers you will have about 10% that will buy your eBook and other affiliate products, so 50 people total. So, if you are selling your eBook for $10, you will make $500. Of course it doesn’t stop there, those people that buy the eBook and like it will most likely recommend it, and you will have a snowball effect where more people keep buying your book and other affiliate products. This is just a rough example that shows you some realistic numbers. Do not ever think that if you build up a huge number of readers that they will all trust you and buy the products that you promote; if it was that easy everyone would be a millionaire by now.