Validate trick set (7)

I believe the answer is:

confirm

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'validate' is the definition.
(thesaurus)

'trick set' is the wordplay.
'trick' becomes 'con' (a con is a fraud or trick).
'set' becomes 'firm' (I can't explain this - if you can you should give a lot more credence to this answer).
'con'+'firm'='CONFIRM'

Can you help me to learn more?

(Other definitions for confirm that I've seen before include "Strengthen" , "Substantiate" , "Ratify; establish" , "Make (provisional arrangement) definite" , "Provide supporting evidence, make definite" .)

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

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