Collocations for sincerity - noun

complete, deep, great, total, utmost
genuine, heartfelt
fake, false, mock
‘Of course!’ I replied with mock sincerity.

apparent
He spoke these words with apparent sincerity.

obvious
emotional
a sense of emotional sincerity in each song

doubt, question
There seems no reason to doubt the sincerity of his beliefs.
There was no questioning his sincerity.

be convinced of
She wasn't yet convinced of his sincerity.

demonstrate, prove, show

with sincerity
sincerity in
He could hear the sincerity in her voice.

in all sincerity, with all sincerity (AmE)
‘Really?’ he asked in all sincerity.

lack of sincerity
His eyes betrayed his utter lack of sincerity.