Aid a gullible person, we're told (7)
I believe the answer is:
succour
'aid' is the definition.
(I know that succour is a more specific form of the action aid)
'a gullible person we're told' is the wordplay.
'a gullible person' becomes 'sucker' (sucker can mean a foolish or gullible person).
'we're told' indicates a 'sounds like' (homophone) clue.
'sucker' is a homophone of 'SUCCOUR'.
(Other definitions for succour that I've seen before include "Comfort" , "Relief in time of distress" , "Give assistance in time of difficulty" , "helping hand" , "Isolated" .)