Reading Tammi Labrecque's excellent Newsletter Ninja, I thought again about finding who my target audience is. This is preached at us constantly, but it's hard to guess from sales just who is buying. I get most sales evenings and weekends, it's true. Then again, most people tend to be busy with things other than searching Amazon for books during weekdays, even if they actually do spend all day reading. So the timing of sales isn't a help.
Then I followed the Amazon review trail of one of my faithful ARC readers and realized that she likes the same kinds of books I do and the same kind I (sometimes) try to write. So from now on, some of my newsletters will be aimed at her specifically.
There's a caveat. That same Amazon trail will reveal if people usually buy books or if they are ARC team members for multiple authors or agencies. If the latter, converting them to paying customers would probably be very difficult, although they could still be useful as dedicated ARC reviewers.
I've occasionally followed a reviewer's trail just to see what s/he says about other books. If a 1-star review is out of the norm for that reviewer, it's likely to be heartfelt and not just a case of a cynical person who is mean to everyone.
As I understand it, reviewers can set their body of reviews to be public or private, so this isn't an invasion of privacy.
Just another angle in attempting to understand readers.