Go bad, getting led astray after advert (5)
I believe the answer is:
addle
'go bad' is the definition.
(addling is a kind of going bad)
'led astray after advert' is the wordplay.
'astray' indicates anagramming the letters.
'after' says to put letters next to each other.
'advert' becomes 'ad' ('ad' can be a synonym of 'advert').
'led' with letters rearranged gives 'dle'.
'dle' put after 'ad' is 'ADDLE'.
'getting' acts as a link.
(Other definitions for addle that I've seen before include "Confuse; become rotten" , "Make rotten" , "(Of eggs) turn bad" , "Muddle or confuse" , "Rot" .)