These were all links to free promotions which I followed from Twitter or the KDP forums. I'm actually glad I didn't pay anything for any of them, as I wasn't particularly impressed. I think there are a lot of authors, mostly in the US, churning out very short non-fiction books. They give them a great title and cover, but the content isn't up to much.
3-Step e-book Ranking System by E. McNew
Can't provide a link as I can no longer find this on Amazon. It may be this one renamed or a taster of it. The author claimed the book would give you secret ways of improving your ebook rankings. She talks about colours of covers - what colours relate to different genres, and what would draw a browser in. I think the sections on each colour must be written in different colours, because on my basic black and white kindle some of this text was pale grey and hard to read. She talks about pen names and pricing. She mentions very briefly the need to edit and format your book and how to upload it to KDP. Then she talks about categorising your book - the essence of this section seems to be to find a small category and put it there, so you have more chance of hitting number one.
The psychology parts were a bit homespun to say the least. The sections on uploading and editing weren't anything much to do with the point of the book. Some of the stuff on categorising and picking keywords was interesting but is covered in more depth on the KDP help pages.
Short, badly formatted, poorly planned.
Author's Quick Guide to Editing your Book by Kristen Eckstein
Needed an edit itself. Several typos in this book, which is unfortunate given its subject matter, and not really acceptable given its brief length. The book talks about whether you should employ a ghost writer (really?), a structural editor or a copy editor. There's a very brief section on making sure you know the difference between affect and effect, compliment and complement etc, and how to use commas. Part way through the author admits this book was written in a day, as part of a challenge to publish a book a week. It shows. it's one of a series of quick guides for authors but I won't be downloading any others, even if they're free.
Knee Pain Cure by Ace McCloud
This book wins an award for the longest ever subtitle which I can't be bothered to type out. I have dodgy knees so when I saw this one for free I downloaded it, hoping to pick up a few tips. It's mostly about dealing with and recovering from knee injuries. Arthritis is given a passing mention. There's a lot about possible surgeries to repair knees, and no real advice for coping with or minimising regular age-related wear and tear. So nothing in it for me, and again, another book which came across as poorly planned.