Largely counterfeit toiletry (7)
I believe the answer is:
shampoo
'largely counterfeit toiletry' is the definition.
'shampoo' can be an answer for 'toiletry'. I am not certain of the 'largely counterfeit' bit.
'counterfeit toiletry' is the wordplay.
'counterfeit' becomes 'sham' ('sham' can be similar in meaning to 'counterfeit').
'toiletry' becomes 'poo' (I am not sure about this - if you are sure you should believe this answer much more).
'sham'+'poo'='SHAMPOO'
(Other definitions for shampoo that I've seen before include "hairdressing" , "Hair-cleansing agent" , "Soapy liquid for hair" , "Hair cleanser" , "preparation for cleaning locks" .)