Compliance, as they say, is advancement (6)
I believe the answer is:
ascent
'is advancement' is the definition.
(I've seen this in other clues)
'compliance as they say' is the wordplay.
'compliance' becomes 'assent' (I've seen this before).
'as they say' indicates a 'sounds like' (homophone) clue.
'assent' is a homophone of 'ASCENT'.
(Other definitions for ascent that I've seen before include "Mountain path" , "Incline" , "Maybe promotion" , "An up-slope" , "Uphill journey" .)