Someone smart, allowed to rise, taken in by corrupt client (9)
I believe the answer is:
intellect
'someone smart' is the definition.
(intellect can mean a clever person)
'allowed to rise taken in by corrupt client' is the wordplay.
'allowed to' becomes 'let' (to let something happen is to allow it).
'rise' is a reversal indicator.
'taken in by' means one lot of letters goes inside another.
'corrupt' is an anagram indicator.
'let' in reverse letter order is 'tel'.
'client' anagrammed gives 'inlect'.
'tel' placed inside 'inlect' is 'INTELLECT'.
(Other definitions for intellect that I've seen before include "Brain" , "understanding" , "Person with brilliant mind" , "Faculty of reasoning" , "Cognitive faculty" .)