Flying Viking, your case demonstrates exactly how it is easy to get a stranger to change seats so that all are satisfied. If she had asked the business class passenger beside her to move to economy, we all know pretty well what the answer would have been!! [see my post above to get my response
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If a request was always for you to move to an equal or better seat there would seldom be a problem, in my experience however that has never been the case.
I have been asked a few times by the flight attendants if I would move, and of course always assist without question on those occasions.