Employer of a shifty ruse (4)
I believe the answer is:
user
'employer' is the definition.
(thesaurus)
'a shifty ruse' is the wordplay.
'a shifty' is an anagram indicator.
'ruse' anagrammed gives 'USER'.
'of' acts as a link.
(Other definitions for user that I've seen before include "Patron" , "Operator; exploiter" , "Consumer" , "Junkie's" , "Someone who exploits another" .)