About the Algorithms
I keep reading about how Amazon's algorithm did this and that. How it buried this book or uses reviews to determine ranking. Here's what I've learned about them.
First, it's not the algorithm. Amazon has at least three – Bestseller, Popularity, and Recommendations – that control what gets displayed on any of their lists and pages.
Second, from our side of the screen, they're all black boxes. We have no direct knowledge of what they use or how they work. Which isn't to say we haven't been able to make some educated guesses based on the data going in and the data coming out.
Are we right? Hard to tell, but what we believe continues to accurately predict outcomes within a narrow range of variability.
Bestsellers
If you start with a specific title, scroll down to see that books sales rank, you can click the links to find the bestseller list for that category. You can also search on the term “bestsellers” to find the master list.
The best seller algorithm uses daily sales units, almost exclusively, to determine a books rating. It uses a weighted average that gives more weight to current sales than recent past. Those sales are also windowed. The algorithm ignores sales numbers that occurred too long ago.
It's why you see a book's ranking drop precipitously about a week or ten days after launching. Authors who spend a lot of time and effort to pump up that first day have little or no support for follow through sales going forward. It's one of the liabilities of pre-orders. Readers like them, but it screws up the title's visibility after launch by front loading all those pre-orders which then get aged out of the ranking calculation.
A common myth holds that the number of reviews matters. That Amazon won't give a sales rank until you get some number of reviews. The most common number I hear is 50. That's patently false. I've had sales rank show up on my books in as little as a day with fewer than a dozen reviews.
One theory holds that Amazon waits for certain days of the week and runs a batch process to update all the product description pages at once. It makes as much sense as anything else.
Key point: Your bestseller rating is a number based on your sales, but your rank is based on everybody else's rank. If your rank is 1000, that means 999 books have a rating number higher than yours at that moment. There's got to be a tie-breaker calculation in there but it's likely to be the variability of sales during the algorithm's window period. They favor consistent sales over spikes. Even relatively low rankings will give you better visibility – and earn more revenue – if they're consistent.
Note that this gets updated hourly and every book in the store gets a new position based on that calculation. For books with a sales rank above 100,000, best seller ranks can change drastically and in unexpected directions. Sure your book may have sold more in the last hour, but with over six million books lower than 100,000, it would only take a few of them moving up to drop your higher rating into a lower rank. If your big sales day earlier in the week aged out of the calculation, today's rank will be lower in spite of the current uptick in sales.
Popularity
If you browse books by category, you'll find the popularity list. This list uses the bestseller rank weighted by price to adjust the book's position on the list. You will occasionally see books with higher sales rank listed below titles with higher cover prices. It's not a big difference, but it's a difference.
The category lists used to be more prominent and more important for ebooks. New Kindle owners had little to go by beyond what genres they liked. As the flood of new Kindle users has waned, this list has fallen in importance for reader driven, serendipitous discovery.
Recommendations
There are a few different recommendation engines. One recommends books you might like at the bottom of a particular book's page. A different list shows up when you just look at the top level of the Kindle bookstore. The selections are context sensitive but based on the books you've bought and even the books you've looked at.
You have some control of these, although getting to the actual settings via a three-dot menu can be aggravating. Once there, you'll be presented with a long list of previous purchases that you can set to use or ignore for future recommendations. If you buy a lot of gifts, this can be helpful.
Promotions
Amazon does promote self-published books without asking for payment. They send out email promos all the time – at least once a week. Genre related titles to the ones you've looked at but not purchased (including your own) feature regularly. It's their way of asking “Are you still interested in this book?” but they recommend other titles from that niche.
They also send out invitations to participate in promotional activities at least once a quarter. The factors influencing that algorithm remain unknown. Almost certainly, you need sufficient presence in the market through the number of books in your catalog and/or your overall sales for them to notice you. Anything beyond that is speculation.
Watch the inbox associated with your account. They'll email you an invitation which you'll need to accept in order to be included. Amazon reps have said that they invite way more people than respond, so keep an eye open. Most of them don't result in much but sometimes a little bit of help is all you need.
Final Point
Amazon does not block books except for some morality issues, mostly putting erotica in the ghetto.
Yes, authors get caught sideways by Amazon. It's rare, but it happens.
It's why you always own your own piece of the internet by having a website and an email list. Those two things will give you a fall back position and you can begin exploring the wide world beyond Amazon.