Worthless paintings returned before retiring (6)
I believe the answer is:
trashy
'worthless' is the definition.
('trashy' can be similar in meaning to 'worthless')
'paintings returned before retiring' is the wordplay.
'paintings' becomes 'art' (I've seen this before).
'returned' shows that the letters should be reversed in order.
'before' means one lot of letters go next to another.
'retiring' becomes 'shy' (I've seen this in other clues).
'art' back-to-front is 'tra'.
'tra'+'shy'='TRASHY'
(Other definitions for trashy that I've seen before include "Cheap and nasty" , "Of no value or quality" , "Shoddy and worthless" , "Shy art - rubbishy" , "Cheap and badly made" .)