Smartens up princess, scruffy without pin (7)

I believe the answer is:

spruces

'smartens up' is the definition.
(to spruce is to tidy or smarten up)

'princess scruffy without pin' is the wordplay.
I cannot quite see how this works, but
'princess' could be 'pr' and 'pr' is found in the answer.
This may be the basis of the clue (or it may be nonsense).

(Another definition for spruces that I've seen is " trees sold recently?".)

I've seen this clue in The Guardian.

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