Decide not to take part in work with unscrupulous seller (3,3)

I believe the answer is:

opt for

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'decide' is the definition.
(thesaurus)

'not to take part in work with unscrupulous seller' is the wordplay.
I cannot really see how this works, but
'not' could be 'o' (I've seen this in other clues) and 'o' is located in the answer.
'to' could be 'for' and 'for' is found within the answer.
'part' could be 'pt' (abbreviation) and 'pt' is located in the answer.
No letters remain.
This may be the basis of clue (or it may be nonsense).

Can you help me to learn more?

I've seen this clue in The Telegraph.

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