If you are struggling with the grade, I'll submit how I look at a mid grade book
1) I look at all four corners. If they are at all ragged, it's dropping into the 5.0 range
2) I look at the spine for checks and tears at the staples. This one is actually furry. It's dipping in the 3.5 range
3) Color breaks. It's got them. depends on severity and frequency. This lots and lots down in the 3.5- 4.0
4) Back cover for stains water damage, tears, other checks, overall rear 5.0
There's lots of other things than can go wrong, or right but these are the basics
Overall, I'm at a 4.0
My opinion of course, just trying to be helpful.