The 'linked' books I received as recommendations were all linked via subject matter. In other words, Amazon looked at the kinds of subjects my buying patterns showed as favourites, and lobbed other books at me they thought I might enjoy. Quite a number of these turned out to be self-pubbed. I didn't expect this, but it's an interesting development. I know that when you submit to Amazon, you are invited to link your book to particular genres or subjects. I'm wondering if that is enough, or whether there is something else you need to do to get Amazon to promote your self-pubbed book to supposedly interested readers.
