Bathroom purchase fake? Not entirely dreadful (7)
I believe the answer is:
shampoo
'bathroom purchase' is the definition.
'fake? not entirely dreadful' is the wordplay.
'fake?' becomes 'sham' ('sham' can be a synonym of 'fake').
'not entirely' means to remove the last letter.
'dreadful' becomes 'poor'.
'poor' with its last letter taken away is 'poo'.
'sham'+'poo'='SHAMPOO'
(Other definitions for shampoo that I've seen before include "Liquid soap" , "preparation for cleaning locks" , "detergent" , "Hotel freebie - Warren Beatty movie" , "cleansing liquid" .)