Evil bank acquires church, honestly! (9)
I believe the answer is:
Here is my best explanation:
'honestly' is the definition.
('sincerely' can be a synonym of 'honestly')
'evil bank acquires church' is the subsidiary indication.
'evil' becomes 'sin'.
'bank' becomes 'rely'.
'acquires' is an insertion indicator.
'church' becomes 'ce' (abbreviation for Church of England).
'sinrely' going around 'ce' is 'sincerely'.
(Other definitions for sincerely that I've seen before include "the last word before signing", "With genuine feeling", "In a genuine way", "Not showing any deceit", "Really", "Last word in letter", "In good faith", "without hypocrisy", "(Yours) genuinely" and "Genuinely, honestly".)