Mistreated a book, second-hand (6)
I believe the answer is:
abused
'mistreated' is the definition.
('abuse' can be a synonym of 'mistreat')
'a book second-hand' is the wordplay.
'book' becomes 'b'.
'second hand' becomes 'used' (I've seen this before).
'a'+'b'+'used'='ABUSED'
(Other definitions for abused that I've seen before include "Reviled, or used wrongly like drugs" , "Insulted; violated" , "Ill-treated" , "vilified" , "Criminally maltreated" .)