[MonkeyScribe]

My book was consistently selling 40 a day for an entire month. (Amazon US) The next month I was selling around 50 until the end of the month where it jumped to 100 a day. The next month it stayed at around 150 for a while, then jumped to 250 then 350. Then that next month it sold 550 each day pretty consistently. Then it jumped to 750 a day for all of Feb. Then it jumped down to 550, then 450 then 350. Rank fell. It was a dramatic drop, not a gentle decline. Now I'm selling about 65 to 70 a day on Amazon US.

My guess? If you sell well, Amazon starts promoting you. At some point they start promoting someone else and your promotions die down.

There's no way I can sell 750 books on my very own. I can't reach that many people by posting on forums or blogs. It wasn't ME. It HAD to be Amazon.

Maybe Saffina's book was listed as 'also bought' on some of the free novels 'selling' really well, so she got a lot of exposure. Then those novels might have gone to "paid" and dropped dramatically down in ranks. That would decrease exposure fast.

Yes, this. The same thing happened with The Righteous, but sped up and I think the whole algorithm shifting moves more quickly now than it used to. There was a time in late March and early April where my book was in the "also boughts" in almost every bestselling mystery or thriller and then it started disappearing and so did the sales. I did no promotion when it was going up, but I received two great reviews going down and they didn't affect anything, so far as I can tell. You can't fight the algorithms. They move like the tide.