Okay, I think I figured something out. People don't want to buy 99c books, but they want to pay 99c for books.
I regularly use Kindle Countdown Deals and typically price my books at 99c for the duration of the KCD. Unless it's a series. Then I put the first book at 99c and the others at like $1.99. This time I made all the books in the OUAD series 99c just to see what would happen. My last KCD for OUAD, I sold a bunch of Wish In One Hand, but not that many of the other books. This time, people are buying all 4 books. Oh, they're still buying more copies of WIOH than the others, but WIOH is the one in the ad, so that's expected.
Additionally, a while back I had the bright idea that if people were buying my books when they were 99c for a KCD, then it stood to reason that they wanted 99c books. Nope. Wrong. I think I actually sold fewer books when they were all regularly 99c then when they were at their usual prices (which, at that time, was $2.99 across the board). And I definitely sold less than when they were 'on sale' for 99c.
Turns out, people want to feel like they're getting a deal. And regularly priced at 99c is apparently not a deal.
Also, I know there's a mindset out there that 99c books are low-quality books. I read a blog post once, by a bestselling author no less, that books priced at $2.99 and under aren't worth reading cuz they obviously all suck or they'd be priced higher. (No their exact words, but that was the gist. And thanks for gisting that publicly, asshole.) But books on sale for 99c don't suffer under the same misconception, I guess.
So, I raised all my prices back to $2.99 and then raised most of them to either $3.99 or $4.99. (Accidental Death, Natural Causes, and Sleeping Ugly are all at $2.99 for the time being. May change that soon.) I still see most of my sales when they're 'on sale', but I think simply having my books priced higher makes those times I discount my books more attractive to buyers.
:shrug: The psychological aspects of book sales. Weeee.
Hope that helps. I'll probably do a numbers post on this sale sometime next week, so y'all can see what's going on. Meanwhile, I have a round of FB posts to do. Catch ya later.