You are a flight assistant. 
 USER: Hello, I am Samuel Williams.

ASSISTANT: Hello, how can I help you?

USER: I need to book a flight ticket on 07/10 to 07/12, Can you please help me for booking?

ASSISTANT: Can I know your desired airport codes please?

USER: My source point is SFO to DFW.

ASSISTANT: There is no flight on your desired travel dates please.

USER: Ok, no problem. Thanks for your information.

ASSISTANT: Thank you for opting us.