Cleaning preparation, fake, poor? Not entirely (7)
I believe the answer is:
shampoo
'cleaning preparation' is the definition.
(preparation for cleaning hair)
'fake poor? not entirely' is the wordplay.
'fake' becomes 'sham' (sham can mean fake or pretend).
'not entirely' means to remove the last letter (most but not all of the word).
'poor' with its final letter taken off is 'poo'.
'sham'+'poo'='SHAMPOO'
(Other definitions for shampoo that I've seen before include "Cleansing agent" , "Hair-cleaning product" , "Hair cleanser" , "Washing preparation (from Hindi)" , "detergent" .)