Who are the ones who usually fly first class? I really think
it's obscenely expensive leh. How many first class seats, on
average, are taken up on a flight?
People obtain first-class seats by upgrading with their frequent
flyer miles also right?
There was once, my brother made an online booking for his seat.
When he checked in at the airport, he wasn't given the seat cos of
some... don't know what problem. But he insisted, cos he had
already made an online booking. In the end they upgraded him to
business class for free. It's SIA. 
