service-for-authors - Sales Rank and Review Monitor - Monitor the sales and review activity for your book or product on Amazon.com
Amazon monitoring service: Amazon sales rank and review reporting service.
If your book has ever sold on Amazon, then it has a sales rank. If the sales rank drops then you have likely had a sales event. You need to know when this happens so you can visit the page and see if you are a best-seller in any category or if you have a review with text that you can use on social media.
You can personally monitor this, but your time will be much better spent in other places, letting our programs be the watch dog you need for this information so you can take immediate action which is the key to keeping sales momentum going. **Your book must be sold through Amazon for this.
If you have a Kindle and a physical book, they will both be included for the one price.