Passenger flights are mainly operated by the Traders Guild, but Academicians also maintain their own, smaller network. Most ordinary purebloods that need to travel buy tickets from them. Such flights are performed by cheap, insignificant ships that pose little danger to us. If we shoot down one such vessel, we can expect to fight many people, but most of them aren't much of a threat. However there is one fine point: do not expect such an attack to be particularly popular if you slaughter and capture civilians (Trader personnel is free game). Passenger ships land mostly in cities, so it's often required to shoot them down to get them.