Offer true love, not at first to be trifled with (9)
I believe the answer is:
volunteer
'offer' is the definition.
('volunteer' can be a synonym of 'offer')
'true love not at first to be trifled with' is the wordplay.
'at first' says to take the initial letters.
'to be trifled with' is an anagram indicator (trifle can mean 'play with' or 'fiddle with').
The first letter of 'not' is 'n'.
'true'+'love'+'n'='trueloven'
'trueloven' with letters rearranged gives 'VOLUNTEER'.
(Other definitions for volunteer that I've seen before include "Willing (or unpaid) worker" , "Unpaid helper" , "One works in an unpaid capacity" , "Opposite of conscript" , "One enlisting of own free will" .)