2. Do you believe it?
3. I think it's hard to believe.
4. It's too good to be true.
5. I don't buy your story.
6. Believe it or not.
7. Really?
8. Are you kidding me?
9. You must be joking.
10. Are you joking?
11. Are you serious?
12. I don't think so.
13. I doubt it.
14. I doubt that he likes you.
15. I am doubtful about that.
16. It's doubtful whether this will work.
17. Don't expect me to believe this.
18. It can't be ture.
19. How is that possible?
20. I never take him too seriously.
21. He is a doubting Thomas.
22. I am at a loss what to do.
23. I feel puzzled.
24. It's a hard nut to crack.
25. You got me.
26. What's to be done?
27. I'm in trouble.