But you've to consider that many customers will download everything that's free. For example, if you've a cookbook in the promo phase and customers have downloaded novels, self help books etc. before and/or after they downloaded your book, you build up "false connections" to these unrelated books. The more downloads you get, the stronger will be these senseless connections. So after the promo phase you've more sales but if you can't hold them up your visibility decreases until your book is dead. Only chance is to run another free promo. The more free downloads you have, the the more "related sales" you need after the free promo phase to get connections to related books and this may take several months. With the free promo you'll take the quick bucks but boycott your long-term success.
PS: It's not clear how the algorithm works exactly and this is just my personal opinion. So I don't want to say that the free promo isn't working for someone else but for me it isn't working.
Indeed, if you just use a simple free book promotion, you may end up having your own book 'connected' to all kind of unrelated books. Not to mention that this will be clearly seen in the 'Customers who bought this item also bought' section of your book and it will alter your sales potential.
The 'secret' is to use a targeted free book promotion and to get on Kindle's list of featured books.
Let's take your cookbook example: it should be promoted to an audience which is really interested in (free) cookbooks. This audience must have already downloaded other cookbooks when they were free on Kindle. And they might download other free cookbooks after they have downloaded your book. This way, your cookbook will be 'connected' to other Kindle cookbooks and not with erotica novels (just an example). Furthermore, a targeted free book campaign will rank your cookbook high in its category and other readers will find and download it. Of course, these other readers are interested in and have downloaded other cookbooks, too, since they are browsing through the cookbooks best-sellers.
The best part is that, your cookbook will not just become 'connected' with other best-sellers in its own category. But, when it will become paid again, it will also rank high on the Kindle cookbooks category page (which, in fact, it is a list of featured items). And I am not talking here about the Top of that category; I am referring to the specific category page where people are navigating from the Kindle menu (left side of the page, if you are browsing the Kindle Store on your PC), when browsing the platform on their Kindle Reader, Kindle iOS/ Android App, or on their PC.
To have an idea about what I am talking about, go to Amazon.com >Kindle Store >Kindle Ebooks > Cookbooks, Food & Wine. Scroll down until you see something like this: '1-16 of 89,058 results for Kindle Store : Kindle eBooks : Cookbooks, Food & Wine' (I attached a screenshot, too). After running a correct (read 'targeted') promotion, you should be able to see your book in this list of featured (read recommended by Amazon) books. From my experience,
this is where the big money is!
Look at these titles: they are all best-sellers now. Look at the last one in this scree-shot. It has only 5 reviews and a general score of just 3.5 stars. But it is a best-seller. I would bet this title has been successfully promoted to a targeted base of readers while it was free. And now (when the book is not free anymore) it becomes a best-seller.
Not to mention that having your book featured on the first page of its category (a/m screen-shot) would mean that the Kindle platform would start promoting it (through targeted emails, recommendations etc.), to other interested readers that don't get to access this page And don't forget that amazon knows very well what each user is looking for; in the description of their A9 Search algorithm, amazon says that they know what you are looking for before you even start searching.
Basically, a successful targeted free book promotion will show the Kindle platform that your book will convert well and it will have a great potential of attracting sales. And this is demonstrated by the high amount of targeted users (remember: amazon knows exactly what is each of their users interested in) which have been attracted by your book while it was free. Statistics show that your book will attract customers when it will become paid, too. And long-term success is not being boycotted; instead it is improved if you are using a targeted audience when promoting your free book.
Of course, there are more benefits coming from a targeted free book promotion: great exposure in a community of interested readers, more chances to receive reviews from people which are interested in what you are writing about, more chances to increase the sales of your other titles (from the same series/ pen name) etc.
Now, the more targeted downloads you get while your book is free, the better all your results will be.