Some Southwest Airlines passengers say a new policy feels like a "fat tax." Kari McCaw says agents stopped her at the ticket counter and told her to buy a second seat or not fly. SFGATE found nearly a dozen viral videos, and several customers described being singled out based on appearance. Southwest ended open seating in January and changed guidance that once made it easier to get a second seat and a refund. The policy says the armrest is the "definitive boundary," and Southwest can require an extra seat for safety. Southwest Airlines declined to comment on staff training or how agents determine whether a customer fits.