Yesterday was a good day at Amazon for (my book). But, it is hard to see how many books they sell. Their stated numbers of books in stock is erratic, as is its correspondence to delayed but related sales rank. I have tried a few times to watch the books in stock but it fluctuates according to no apparent logic.
Amazon’s “in stock” numbers are not always true. This is only my opinion but I think they use those to create a sense of urgency in buyers, giving them a stronger desire to buy (i.e. “Only 1 left in stock”). Amazon doesn’t stock most print on demand books. In fact, they don’t even stock some traditionally published titles, either. Our printer and Ingram (the world’s largest book distributor) both ship some books directly to Amazon’s customers, even using an Amazon.com return address label.
The only reason Amazon would have a copy of a POD book in stock is if a customer returned a book, if the author or publisher signed up to have Amazon stock that book for a fee (plus the publisher/author must pay for shipping to send books to Amazon, or to have the unsold books returned), or if Amazon had to order a copy for some odd reason. That has happened in the past when they had errors in their listings that said a book was not in stock at all or was otherwise unavailable when it was. In those cases, Amazon may order a copy just to “fix” the listing. (Seems it would be faster and cheaper to simply FIX the listing manually, right?)
You can search Amazon’s site by publisher name and the books will appear in a variety of ways, despite the fact that they’re all being printed and shipped in the same way, and all have the same real availability. One book will say “in stock.” Another will say “ships in 2-3 weeks.” In the case of many POD books, neither of those is even remotely true because the book’s printer is shipping to Amazon’s customer directly, bypassing Amazon’s warehouse altogether. And, the process does NOT take 2-3 weeks. The orders are automatically sent by Amazon to the printer (the largest POD printer in the world), and they quickly print and ship those out.
I would never try to estimate sales based on Amazon’s webpage information because, in many cases, their information is simply not true. Worse, I don’t think they care. When we have complained about listing errors in the past, we have received automated responses back that didn’t answer our question, or that basically told us Amazon can list/price books at their discretion (even though they must still pay the publisher or printer the amount specified by that publisher or printer).