How To Research Categories, Sales Rank & Keywords For Amazon Kindle Sales | Author Marketing. Author marketing is actually kind of fun. It allows me to take all the bits from other kinds of marketing that I already understand and put them together to make a brand new form that helps with book sales. Today we are going to be talking about doing research for your Kindle eBooks for sale on Amazon. In some ways doing Amazon ranking research is just like researching for Google SEO keywords.