here you go - http://www.msn.com/en-us/money/comp...d-seats/ar-BBzJLPS?li=BBmkt5R&ocid=spartanntp
“Including advance-seat-assignment charges among the ‘basic ancillary service’ fees that must be disclosed as part of initial fare displays makes no sense,” the airline wrote to the Department of Transportation. “Every ticket, of course, guarantees a passenger a seat on the plane, with no additional mandatory seat-assignment charges."
Later in the filing, United Airlines expanded on its promise to regulators that it guarantees every ticketed passenger a seat.
“Importantly, every passenger who buys a ticket on a United flight or a flight on any of United’s partners or competitors in the United States will be assigned a seat at no additional charge (though in some cases this will still happen at the gate),” the airline wrote. “Therefore, the rule does not need to prescribe how carriers must disclose charges concerning advance seat assignments because passengers need not purchase this service to receive a seat assignment.”
As I found out the hard way, Lufthansa, one of Uniteds partners does charge extra for an assigned seat. You can select whatever seats you want during the purchase process, doesn't mean they wont scatter your party across middle seats throughout the plane upon checkin. Ironically, if you fly the same LH flight on a United ticket number, you do have assigned seats.