How Amazon lists a title and the available/in-stock status on their website is ultimately up to them. Amazon's purchasing decisions are supported by an algorithm that is proprietary to Amazon. In choosing to stock titles or even show products as available on their sites, Amazon considers many pieces of information about your book. Factors in a decision to stock a book may include a discount (with a maximum wholesale discount of 55% being most favorable), whether a book is returnable, product page views, and sales history. Even print-on-demand books may not show an 'in stock' message at Amazon. Amazon may also list your title as available through third-party vendors.
For additional information about Amazon's title status messaging, please visit the Amazon website.
Requirements for Amazon.com
*We are only able to notify Amazon.com, Amazon.ca, and Amazon.co.uk once a title has been in distribution for at least 30 days. We then allow Amazon’s website enough time to update once a title’s metadata is sent before our initial notification.
On Amazon, a lower ranking for a title indicates more sales for that particular item. The calculation is based on Amazon.com and Amazon.co.uk sales and is updated each day to reflect recent and historical sales of every item sold on Amazon.com and Amazon.co.uk.
Sales projections and trends take an active role here, which is why a book's ranking can leap from 90,000 to 50,000 in the span of 24 hours or less. What this means is that recent activity (i.e. purchases) for that book is trending higher than those 40,000 books it just surpassed. But, since the activity of those 40,000 other books ranges from slow to stagnant, one or two orders are sufficient to catapult a ranking.