The cover of the Eighth Five-Year Plan book should be a little old, but it should not be rotten.
Don't worry about the pages turning yellow. Any old book will be like this if it is kept for a long time, as long as it is not damaged.
I often buy some books with nine grades there, and the appearance is still quite good. What I bought was published ten years ago, but the cover is a little old and everything in it is as good as new.
If you are strict about appearance, I suggest you communicate with the shopkeeper first.