Any booking that involves the crossing of a border is only bookable with the appropriate travel documents, in most cases, this is a valid passport.
Exceptions to this may include domestic travel where the client doesn't leave their home province or state, and occasionally travel within their own country. However, domestic travel may soon require passport documentation.
We might also note that travel is often unpredictable, and circumstances may arise where a border is crossed because of unforeseen events, such as an emergency.