Unfortunately, scoundrels use naivety (13)

I believe the answer is:

credulousness

'naivety' is the definition.
(credulousness is a kind of naivety)

'unfortunately scoundrels use' is the wordplay.
'unfortunately' is an anagram indicator.
'scoundrels'+'use'='scoundrelsuse'
'scoundrelsuse' with letters rearranged gives 'CREDULOUSNESS'.

I've seen this clue in The Telegraph.

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