believe
1. believe it or not
e.g.: Believe it or not, I'm feeling quite homesick.
I was already a university teacher, believe it or not, when I was only nineteen.
2. believe (you) me
e.g.: She's the worst singer in the world, believe me.
A: You should write to the firm and complain.
B: Believe (you) me, I will.
3. … I believe?
e.g.: A: Penny, I believe?
B: Yes.
A: Then come in, please.
A: Julia, I believe?
B: No.
A: I'm sorry, who is it, please?