Dodgy detective excelled over good person (9)
I believe the answer is:
dishonest
'dodgy' is the definition.
'detective excelled over good person' is the wordplay.
'detective' becomes 'di' (Detective Inspector abbreviation).
'excelled' becomes 'shone' (I've seen this before).
'over' is a charade indicator (letters next to each other).
'good person' becomes 'st' (saint).
'di'+'shone'+'st'='DISHONEST'
(Other definitions for dishonest that I've seen before include "Not on the level" , "Corrupt" , "Untruthful - mendacious" , "Mendacious like hedonists" , "Not straightforward" .)