I read the article and noted that it was written some 4 years ago. Presumably Amazon has filled some of those holes. I think most people also now realize the difference between a real bestseller and a give-away. But there are always ways to manipulate Amazon's algorithms. I shared a
blog post from a writer named C.S. Lakin who uses canny genre choices to sell books. If you look as far as the comments you'll see that she herself was accused of using other writers' stories and cover art illegitimately, but that, IMO, is a separate issue. Her argument was that genre sells. There are only so many sweet Colorado romances out each year, for example, but there's a devoted readership that will buy anything in the category, especially if it's visible at the top of the category. So you look for under-served genres that sell well, she argues, read a few successful examples, and write your own, modeling your cover on the bestselling covers in the genre.
But the whole piece, if you read it, raises a bigger issue: What books do we choose to write? That writer chose to write books she believed would sell well. It's a sensible business model for people who regard books as widgets, not literature, and who have the talent and speed to churn out lots of titles. That's not what drew me to writing, though, and it's not a model that would suit me I'm not fast, so I figure I'll only have time in my life to write so many books; so they'd better be books I really, really want to write.