Regarding quality, I have noticed a considerable decline in non-on-demand quality of paperback books in recent years as well. Paper is often really bad, printing quality even worse. Very often the text is grayish pixelated, I'm guessing this is because the publishers have stored some subpar digitized version of prior editions, which on reprints comes out like an ereader from 20 years ago.

I often specifically look up old or first print editions of books (paperback or hardcover) and then buy them used from Abebooks etc.

However, the quality of the on-demand books via Amazon is hit and miss. It's not universally bad. Sometimes it is very good paper and sharp print. Sometimes it is cheapish white copy paper. The covers are universally bad. In Berlin they apparently come from Poland.

I also got on demand books in similar qualities from other German book sellers (buecher.de for example). On their page at least it's somewhat recognizable that it will be on demand, because they have some details about the manufacturer (themselves in this case).

I'm not necessarily against those on demand books, but I would really like if Amazon and other sites would

- let me know when I have to expect those books

- customize the quality options (e.g. paper color)