One who employs a clever ruse (4)
I believe the answer is:
user
'one who employs' is the definition.
(I've seen this before)
'a clever ruse' is the wordplay.
'a clever' indicates anagramming the letters.
'ruse' is an anagram of 'USER'.
(Other definitions for user that I've seen before include "Manipulative woman" , "Drug addict (colloq.)" , "One who exploits others" , "Drug addict (informal)" , "Patron" .)