Let me toss this in, just to show you how things can be manipulated.
I recently received a newsletter from an author whose books I love. She has a new one out and she was offering it at 99 cents. I bought it, but I felt bad for her because I would have been perfectly willing to buy it for $3.99, the regular list price. The only advantage to her of offering that huge discount was if a large number of people on her mailing list immediately bought the book because it was 99 cents and the rank in the Amazon store rose substantially. But as we know, positive replies to mailings hover at very low percentages. So it was a gamble for her.
So she upped her chances. She ran an Amazon ad for the new book. She also offered the first book in the series free, and the first four books in the series in an omnibus at 99 cents, again, basically free. I felt she left a lot of money on the table to gamble that rank or the bargain prices would make up for selling the latest in her series and four other books at a reasonable price.
And yet...today her new book has a #1 Bestseller tag in "Tudor Historical Romance." It's also high in the ranks as a "Victorian Historical Romance." She writes Regencies, and this story takes place during Napoleon's last stand, but somebody at Amazon doesn't care.
So, diddling with the price, using false categories, getting newsletter sales to boost ranking, adding in an Amazon ad, and basically giving away four more books got her this wholly inaccurate tag and she's under 2k in the whole Amazon store and in the top 100 in the fake categories. Which presumably will give her much more visibility in the store, and eventually will result in more sales.
This really makes me want to rend my garments and wail to the moon. If I were looking for a Tudor historical romance, this book would not be it. And I love her books.