I went to a discussion of Michele Obama's "Becoming" the other day. A person in the group mentioned "The Righteous Mind" by Jonathan Haidt as a book that really helped in understanding those with political or religious views strongly different from one's own. That sort of personal, direct recommendation has often paid off for me and I memorized the title, telling myself to take a look at the book. I did remember the title and looked up the book. I got the message "You already own this item". In fact, I had bought the book in 2014.
I don't spend much time on poetry but sometimes, it comes up. Excellent poetry can make my day. I get lifts from Billy Collins, Mary Oliver, Ogden Nash, George Bilgere. I have run into a couple of mentions of Billy Collins' "The Rain in Portugal." Again, I remembered the title. Again, I thought I would treat myself to the book. Again, I found Amazon wouldn't sell it to me. "You already own this item." I bought the book in 2016.
I am approaching 3,000 books in my Kindle archive. I don't expect myself to remember every item I have purchased. I get two or three Kindle ads per day. Most days, I have the patience to look at what is offered with some calm, rather than just deleting. Sometimes, something I want is offered at a very low price. Still, I think it is a good sign that Amazon has the coding in place to block a 2nd purchase of something I already own.