1. “Are you sure about that?”
2. “May I share my view on that?”
3. “Is it possible that there is another approach/solution/source here?”
4. “That’s generally true, but I wonder if it is true in this situation.”
5. “Tell me your thinking on that approach/conclusion, will you?”
6. “Are you thinking that doing that will get you what you really want?”
7. “I wonder if we have all the facts/data on that, yet.”
8. “How can I most help you, right now?”
9. “When/where did you decide that is/was true?”
10. “Hmm. That’s very interesting. Will you educate me on that and why you see it that way?”
source: http://topten.org/top-ten/the-top-10-ways-to-correct-someone-gracefully/
