People who take a cello or something on the plane have to pay for 2 seats, they sit in one and strap the cello into the other. But a person that spills over into the second seat is being treated unfairly if they have to pay for more than one of the 2 seats they are occupying. I think they should have a tester seat with solid sides at the halfway point of the armrests and if you touch both sides (or can't fit in at all) you must buy a second ticket, because otherwise you WILL infringe on the space of the people next to you.