A few years ago my connecting flight from LAX to LAS was cancelled (mechanical). The AC agent said there was an open seat on US Air, but she (for unexplained reasons) could not interline me. I had to call US Air and make all the arrangements, the AC agent did give me a card with the fare breakdown and I did fly on US Air. The US Air agent asked if the AC agent was new--NO, she had 13 years on the job.