One making a choice -- second person at the polling station? (8)
I believe the answer is:
selector
'one making a choice' is the definition.
(I've seen this in another clue)
'second person at the polling station?' is the wordplay.
'second' becomes 's' (common abbreviation).
'person at the polling station?' becomes 'elector' (someone voting in an election).
's'+'elector'='SELECTOR'
(Other definitions for selector that I've seen before include "A chooser of electors" , "One who chooses" , "Corselet (anag.)" , "Person choosing (team)" .)