Boomer: My certificates have written in red print on the front: "VOID IF SOLD, BARTERED OR EXCHANGED FOR COMPENSATION" so I don't have any problem with giving them away. Also I think that it is not the passengers responsability to be aware of all the details in the fine print on the back, and it has been my experience that ticket agents don't worry a lot about it either. My advice is try it , what have you got to loose?