Cleaner pretended to work up to the beginning of October (7)
I believe the answer is:
shampoo
'cleaner' is the definition.
(shampoo is a kind of cleaner)
'pretended to work up to the beginning of october' is the wordplay.
'pretended' becomes 'sham' ('sham' can be a synonym of 'pretended').
'to work' becomes 'op' (abbreviation for opus).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'to the beginning of' indicates taking the first letters.
The initial letter of 'october' is 'o'.
'op' in reverse letter order is 'po'.
'sham'+'po'+'o'='SHAMPOO'
(Other definitions for shampoo that I've seen before include "Soapy liquid for hair" , "Washer for locks" , "Cleaning fluid" , "detergent" , "Hair-cleaning product" .)