He ladles out compliments to everyone, but he’s not really sincere.

他见人就大加吹捧, 但并非出于诚意。

As an earnest of my good intentions I will reconsider your request.

我一定重新考虑你的请求以表示我的诚意。

I don't believe in Tom's sincerity; but this is inter nos.

我不相信汤姆是有诚意的; 不过这是不能对外人讲的。

His bona fides was questioned.

人家怀疑他的诚意。

His bona fides are unquestionable.

他的诚意不容置疑。