Did Polish brand start to invent junk? (9)
I believe the answer is:
burnished
'did polish' is the definition.
(burnishing is a kind of polishing)
'brand start to invent junk?' is the wordplay.
'brand' becomes 'burn' (brand can mean to burn a mark into something).
'start to' says to take the initial letters.
'junk?' becomes 'shed' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The first letter of 'invent' is 'i'.
'burn'+'i'+'shed'='BURNISHED'
Can you help me to learn more?
(Other definitions for burnished that I've seen before include "shone" , "made lustrous" .)