Customer finally ensured treatment... (3,4)
I believe the answer is:
end user
'customer' is the definition.
(I've seen this before)
'ensured treatment' is the wordplay.
'treatment' indicates anagramming the letters (letters treated or processed differently).
'ensured' anagrammed gives 'END-USER'.
'finally' acts as a link.
This may not be right. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for end user that I've seen before include "ultimate consumer" , "Recipient of product sold" , "last link in the chain" , "Product's final owner" , "One who finally receives a product" .)