Teachers are always wondering about who read the assignment. It happens that one student looked diligently at every word but doesn’t remember or understand what was written. Another knows from tv or general knowledge and does well on a test without reading the assignment. It is not always clear what "reading" is.
There are special wrinkles about books a person buys but doesn’t read. Why did they pay good money if they aren’t going to read what they bought? Maybe later. Maybe they have been too busy. Maybe they learned something about the book or the author that turned them off. Very possibly, some other book, or movie, or project claimed their attention and then they forgot about the book.
I have certainly withdrawn books from the library and returned them later unread, sometimes unopened. I have about 350 books on my shelves but I am not reading them since they are not in my Kindle. The little device is easy to carry with me and it allows me to switch between books quickly and easily without taking a step. My paper books are getting lower and lower priorities. These are the same books that have survived culling and weeding many times.
I have experienced going into a bookstore, finding an interesting book and buying it. When I get it home, I find I already have a copy on the shelf but I haven’t read it yet. I guess if I had read it, I would remember having done so. I have also experienced deciding I didn’t need a book I have bought and wasn’t going to read it so I donated it to the library for their money-raising sale. Yep. I went to the sale, found that good book, bought it and then discovered it was the book I had donated.
I am not inclined to find a system for preventing these purchases that don’t lead to a fully read book. I continue to feel that having the freedom to add a book that I may read is worth the damages and waste that comes from exercising that freedom. I have about 200 books in my Kindle and I may not ever read some of them. But I have them if I get around to wanting to. When I learn of the existence of an interesting book these days, I often look at its rating on the Amazon.com site. I may read the most positive and most negative comments readers have made about the book. I may download a free sample of the book. I may add it to a wish list (133 items just now) and a ‘save for later’ list to try to give myself a note about a book that I ought to get around to. But sometimes, I just buy it. My way has worked pretty well for a long time and I think I will stick with it.