Employer in House rebuffed (4)
I believe the answer is:
user
'employer' is the definition.
(someone who employs or uses something)
'in house rebuffed' is the wordplay.
'in' says the answer is hidden in the clue.
'USER' is hidden within 'house rebuffed'.
(Other definitions for user that I've seen before include "One who exploits, to be sure" , "Someone who exploits another" , "Junkie's" , "Manipulative woman" , "One who exploits others" .)