Hi @booknut7,
I use Biblio’s Pro Routing service, so changing the sold book’s status to “Sold” in my spreadsheet and uploading it to Biblio automatically removes/sets to zero my offer on Biblio, Amazon and Alibris. But I am going to keep tabs on the sold books to make sure they are actually deleted from Amazon, to be on the safe side, as you and others have recommended.
I’m doing FBM; I would never let Amazon handle my books! 
I have no specialty, although I do get a lot of scholarly books. (Sadly, virtually all the scholarly/university press books are gated on Amazon.) “Grab anything that looks interesting” is my scouting technique; it’s worked for me so far.
I’ve been scouting for bookstores most of my adult life, but online on Biblio (and Alibris, though sales there are few) for a couple years. I finally took the plunge to get on Amazon a couple months ago, and listed my first books in mid-January.
I have decided to start by limiting myself to $50 and under books on Amazon, since I’ve heard so many horror stories about returns, item-not-received, and book-jackers. I’ve already had one return, but no “not-received,” and the Paper Cavalier and Ergode people have ordered but not caused any trouble.
I’m still working on getting all the <= $50 books to appear on Amazon. It’s quite a struggle.
What witth the above restriction, plus the many gated books, and books that are not appearing for unknown reasons, I have a stock of only about 600 books on Amazon as yet.
Now you know more about me that you wanted to know, I’m sure. 
Thanks for your good wishes, which I return to you x10.