I have a question regardign the 2 pre-Conditions (login and profile).
Are we suppose to show them in every sequence diagram or just once ?
How are the rest approaching it. I have done a sequence diagram for each login and profile creation. But I am confused whether I should show them in each of the other use-cases like price, change, pay etc.
There are some cases in which you must return to a specific page, like when you want to change an itinerary.
So, you must handle the end of sequence diagram according to the case. You should also note that the end user is not the starter of login in every case. Sometimes the system starts the login use case. IMO, you should include the login and profile creation in every use case that uses them.
But, I am in the same situation as you are: designing phase 2. Maybe other people can say something more appropriate.