Publisher’s way of advertising obscure book (5)
I believe the answer is:
blurb
'publisher's way of advertising' is the definition.
'obscure book' is the wordplay.
'obscure' becomes 'blur' ('blur' can be a synonym of 'obscure').
'book' becomes 'b'.
'blur'+'b'='BLURB'
(Other definitions for blurb that I've seen before include "Publisher's text on book" , "Enticing paragraph" , "Publisher's book description" , "Book jacket commendation" , "Publisher's puff" .)