Bill reasonable? Make correct! (6)
I believe the answer is:
adjust
'correct' is the definition.
(I know that correct can be written as adjust)
'bill reasonable?' is the wordplay.
'bill' becomes 'ad' (advertisement stuck on wall).
'reasonable?' becomes 'just' (associated in meaning).
'ad'+'just'='ADJUST'
'make' acts as a link.
(Other definitions for adjust that I've seen before include "Calibrate or regulate" , "Adapt, regulate" , "Arrange, put into proper position" , "Make slight corrections to" , "Change slightly to fit" .)