About a year ago my wife and I were flying YYZ-YVR booked in Tango and had paid for seat assignments. When we went to check-in, the agent noticed that others had been put in our seats for some reason. The agent was so incensed that she picked up the phone in front of us and called a supervisor and said that she had an Elite checking in on a Tango fare, the reserved seats had been taken from us and she wanted to upgrade us. A few minutes later we had our J seats and were on our way. A most satisfactory solution from my point of view!

As a double bonus I received a refund of the $15/seat we had paid for the seat assignments!