In 2007, BA made a mistake in their pricing of a sale offer. They advertised (IIRC) certain flights for 25% off. Their mistake was when you came to book those seats, instead of the 25% reduction, they mistakenly had reduced the fares by 75%! It meant myself and Mrs.M went to HKG return in Y, ( no availability in higher cabins), for £125 each, all in. Which was marvellous, because when we boarded, Y was only a third full. We both had a row of 3 to ourselves. Rather good value I thought! :-)