Who’s quiet, working to pilfer? (10)

I believe the answer is:

shoplifter

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'who's' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.

'quiet working to pilfer?' is the wordplay.
'quiet' becomes 'sh' (both can be said to tell someone to be quiet).
'working' indicates anagramming the letters.
'to'+'pilfer'='topilfer'
'topilfer' is an anagram of 'oplifter'.
'sh'+'oplifter'='SHOPLIFTER'

Can you help me to learn more?

(Other definitions for shoplifter that I've seen before include "Thieving customer" , "A petty criminal" , "Criminal (in a retail context)" , "Robber" , "guilty party" .)

I've seen this clue in The Times.

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