More sordid joint? That's right! (7)

I believe the answer is:

seamier

'more sordid' is the definition.
('seamy' can be a synonym of 'sordid')

'joint? that's right' is the wordplay.
'joint?' becomes 'seam' (seam is a kind of joint).
'that's' becomes 'ie'.
'right' becomes 'r' (common abbreviation).
'seam'+'ie'+'r'='SEAMIER'

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

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