Crossword Genius

Maintains secret retro look I’d found in boutique (5,1,3,2)

Ross

I believe the answer is:

keeps a lid on

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'boutique' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'maintains secret retro look i'd found in' is the wordplay.
'maintains' becomes 'keeps' ('keep' can be a synonym of 'maintain').
'secret retro look' becomes 'alon' (I am not sure about this - if you are sure you should believe this answer much more).
'found in' indicates putting letters inside.
'alon' going around 'id' is 'alidon'.
'keeps'+'alidon'='KEEPS A LID ON'

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I've seen this clue in the Sydney Morning Herald.
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