Person choosing a little carrot, celery going the wrong way (7)
I believe the answer is:
elector
'person choosing' is the definition.
'a little carrot celery going the wrong way' is the wordplay.
'a little' indicates a hidden word.
'going the wrong way' shows that the letters should be reversed in order.
'rotcele' is hidden within 'carrot celery'.
'rotcele' in reverse letter order is 'ELECTOR'.
(Other definitions for elector that I've seen before include "Citizen with a right to vote" , "Voter - old German prince" , "Crosses" , "who's making his mark?" , "Old Saxony, Hanover ruler" .)