The most common and most likely answer to this crossword clue is the 8 letter word REORDERS
I've seen this crossword clue in Independent
R
E
O
R
D
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S
Buddy explains!

The straight part
We know that "books again" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case books again = reorders.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does REORDERS mean?
REORDERS verb- To place in a new order; to rearrange.
- To order (a product, etc.) again.
- To order or command again; to repeat an instruction to.