Thank you for thinking of me.
At that time I am not available. I’m sorry.
Thank you for the invitation.
I believe I do not have skills to do this well. I see two possibilities:
1. I can recommend another person, who may be able to help you.
2. If you accept that I need extra time to learn more about this, I will
be happy to try to help.
Thank you. I feel honoured that you think of me in this regard.
I need to know more. May I please ask you these 3 questions: