I've been getting emails from people who are so frustrated that they cannot get the online bookstores to remove their canceled PA books. I am one among them that is extremely frustrated. I contacted PA back in 05 and they said they could do nothing about it. I then contacted Lightning Source who said my books were listed as out of print and they were not selling them. I contacted Amazon several times requesting they take my books down, that I am the author and copyright holder and that I no longer give them permission to advertise my out of print novels. Nothing. No help at all.
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They're not "advertising" your out-of-print novels. If anything, they're reserving a space so when a used bookseller finds your book at a thrift store, yard sale or donated to them by a friend of relative (I've sold on Amazon and had BOXES of books given to me), they can list that copy as a "used for sale" copy under your the title of your book. If they did delete it, an Amazon "Pro Merchant" reseller who finds a copy to sell could ADD A NEW LISTING for your book on Amazon just so he could sell it. I can't imagine Amazon would ever remove such a listing once it's there, short of a court order or similar thing.
But I'm pretty sure you (but I don't know how to do this) can sign up on Amazon as the author of the book and put an "Author's Note" on that page where you can tell people the book is out of print, will stay out of print, and if they want to buy a copy to NOT contact you, their only chance is to wait for some bookseller to list a used copy. If nothing else, I KNOW you can sign in/sign up as an Amazon customer and start a "Customer Discussion" where you say "I am the author" and say those other things.
Honestly, I don't think you do. Here's the way I think it works. If even one copy of your book was bought by a reseller, for whatever reason (before your PA contract was cancelled), that reseller can then post it for sale on Amazon (usually at an ungodly expensive price, of which you get zero). Why do they do it? I have no idea. But somebody must be making some money on the deal somewhere.
Generally it's called capitalism, but more specifically it's called "throwing crap on the wall and seeing what sticks." I have to admit I've done it. If I have a book I want to sell and I can't find any other copies for sale anywhere online and no history of what used copies may have sold for, the most profitable thing is to "assume" it's rare and valuable, set some high price for it, and see if it sells. One can later lower the price if it doesn't sell, and that's better (for me the seller) than settting a lower price initially, see it sell immediately, and wonder if it would have sold for a much higher price.