Hello!
Hello, how can I help?
I am wanting to take a flight and was wondering if you would be able to help me out.
Where are you departing from?
I will be departing from Pittsburgh.
Where are you going to?
I would like to go to San Francisco please.
On what day do you want the plane to arrive?
Let's shoot for May 12th.
Right, I found an Economy flight with United for 200 credits
 that takes 5 hours to get to San Francisco.
That sounds good.  Is there anyway I could fly with Delta instead?
Unfortunately there are no flights that match your search. Would you like to change any of your criteria?
No I was wanting to fly Delta but if that isn't going to be possible I will have to make a sacrifice.  Let's go with the flight with United that you found.
Thank you and goodbye!