Bad to rent — bad (6)
I believe the answer is:
rotten
'bad' is the definition.
('rotten' can be similar in meaning to 'bad')
'to rent bad' is the wordplay.
'bad' indicates anagramming the letters.
'to'+'rent'='torent'
'torent' anagrammed gives 'ROTTEN'.
(Other definitions for rotten that I've seen before include "Decaying - quite putrid" , "Decayed or detestable" , "Lousy" , "Decayed or morally corrupt" , "Nasty" .)