If bad, they would invoke something better (3,5,3,4)

I believe the answer is:

the devil you know

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'if bad they would invoke something better' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'if bad they would invoke something better' is the wordplay.
'they would invoke' can be anagrammed to 'THE DEVIL YOU KNOW'.
However, I am unsure how the anagram is indicated.

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I've seen this clue in The Times and The Sunday Times.

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