Preparation for locks is fake, low-quality, mostly (7)
I believe the answer is:
shampoo
'preparation' is the definition.
(I know that shampoo is a type of cleaner)
'is fake low-quality mostly' is the wordplay.
'is fake' becomes 'sham' (sham can mean fake or pretend).
'low-quality' becomes 'poor' (I've seen this in another clue).
'mostly' means to remove the last letter (most but not all of the word).
'poor' with its final letter removed is 'poo'.
'sham'+'poo'='SHAMPOO'
'for locks' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for shampoo that I've seen before include "Liquid that goes to your head?" , "treat shock?" , "My partner may be set" , "hairdressing" , "Soap for washing hair" .)