Employed, but taken advantage of (4)
I believe the answer is:
used
I believe this clue is a double definition.
'employed' is the first definition.
('use' can be a synonym of 'employ')
'taken advantage of' is the second definition.
(use can mean to exploit or take advantage of)
'but' acts as a link.
(Other definitions for used that I've seen before include "That's not new" , "no stranger" , "Was treating" , "with some traffic" , "Went through" .)