Ballot fixing true? One is making things dirty (8)
I believe the answer is:
polluter
'one is making things dirty' is the definition.
'ballot fixing true?' is the wordplay.
'ballot' becomes 'poll' (I've seen this before).
'fixing' indicates an anagram.
'true' anagrammed gives 'uter'.
'poll'+'uter'='POLLUTER'
(Other definitions for polluter that I've seen before include "One spoils" , "Ecologically, the one who should pay" , "who spoils the atmosphere?" .)