Shrewd acknowledgement of service is a criminal act! (3-7)

I believe the answer is:

fly-tipping

'a criminal act' is the definition.
(illegal dumping of rubbish)

'shrewd acknowledgement of service' is the wordplay.
'shrewd' becomes 'fly' (fly can mean shrewd or astute).
'acknowledgement of service' becomes 'tipping' (acknowledgement of service from a waiter).
'fly'+'tipping'='FLY-TIPPING'

'is' acts as a link.

(Another definition for fly-tipping that I've seen is " Unauthorised disposal of waste materials".)

I've seen this clue in The Guardian.

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