At any rate, I don't know for certainty that I'm a harder grader, but I believe that it's the case based on reactions I get when I give the speech that I'm about to give.

不管怎么，虽然不是特确定我评分严格，但相信应该就是这样,根据我每次说这些话时得到的反应来说。

耶鲁公开课 - 死亡课程节选

And our third example touches on not when you are expressing a level of certainty,

接下来的第三个例句并不是用于表示某种程度的肯定，

I'm sure 课堂 - SpeakingMax英语口语达人