Having recently finished my YA trilogy, I was about to publish the last book in the series on Amazon and put it into the same categories as the first two (you get a choice of four) when I noticed the Medical Thriller category. This may be a new addition to the fiction thriller genre (Ebola influenced?) or I might have missed it when publishing the previous two books (busy day influenced). I felt it was a good category to put my trilogy into, so I did.
The result has been an increase in sales. This could also be due to the fact that the trilogy is now complete and all three books are published. It’s frustrating to read the first two books of a trilogy and not be able to find the last one, so I usually wait to download all of them at the same time. I suspect it’s a bit of both. Anyway, if your sales are sluggish, try changing the category – but do be careful that it suits your book. Here is what Amazon’s Author Central has to say about this:
How frequently should I change my books’ categories?
In general, you should not need to change your books’ categories on a regular basis. Instead, you will want to make sure that all of your books’ categories are as accurate and specific as possible. Every now and then, new categories are added and so you will want to check back once a quarter or so to make sure your books are still categorized as accurately as possible. You should also make sure your categories are as specific and accurate when you have a new book or edition published.
Changing your books’ categories too frequently may confuse customers browsing for books. Making too many changes to a book’s categories too frequently may result in you being prevented from making further edits to your categories in Author Central.
Why did my Author Rank change when I updated my categories?
Your Author Rank is based the categories that your books are found in. As your books automatically inherit all parent categories of your subcategory selection, placing your books in as specific (i.e. as deep) a category as possible will have a positive impact on your Author Rank.
On your Author Page, your 3 highest Author Ranks are displayed. Placing your books in as specific categories as possible will result in higher Author Ranks being displayed to customers.
As of 26th October 2014, all three books in The Finding Trilogy are in the Kindle top 100 paid Amazon UK Medical Thriller category, (at numbers 4, 7 and 8) about three weeks after the last book was uploaded.
So it seems to be a good idea to check Amazon’s categories every three or four months to see if a new one has been added and whether it is worth your while making a change.