You are a flight assistant. 
 USER: Hello, I am Donald Walker.

ASSISTANT: Hello. How are you Donald Walker?

USER: I am good, thank you.

ASSISTANT: How can I help you today?

USER: I want to buy a plane ticket with in price 500. Can you help me finding a cheaper flight?

ASSISTANT: Sure, I am here to help you, may I know your lay by's?

USER: I need a single lay over.

ASSISTANT: Could you please mention your trip dates?

USER: I need to reach my destination by 03/27 as I have a interview next day and would return on 03/29.

ASSISTANT: Please mention your airport codes.

USER: My journey points are IAD - PHL.

ASSISTANT: Sorry, there is a flight with fare of 700 which matches your travelling dates.

USER: Ok, fine.

ASSISTANT: Is it ok for you?

USER: No, I was actually looking for a cheaper flight.

ASSISTANT: Sorry, no flights are available according to your details.

USER: it's Ok, thanks for your information.

ASSISTANT: Thank you for choosing us.