Quakerism's not converting doubtful characters? (8,5)

I believe the answer is:

question marks

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'doubtful characters?' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'quakerism's not converting' is the wordplay.
'converting' indicates anagramming the letters.
'quakerisms'+'not'='quakerismsnot'
'quakerismsnot' with letters rearranged gives 'QUESTION-MARKS'.

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

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