Evil trader's filthy mouth? (5,5)

I believe the answer is:

river delta

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'mouth?' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'evil trader's filthy' is the wordplay.
'filthy' indicates an anagram (messy letters).
'evil'+'trader'='eviltrader'
'eviltrader' with letters rearranged gives 'RIVER DELTA'.

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

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