just done a flight and on gets a guy on crutches assigned to an emergency exit row because he told check in staff he needed room to stretch his leg. i moved him and he wasnt happy , and i left him where he was for the rest of the flight because it would have been too much messing in case of unscheduled diversion etc. as crew, i will move anyone i dont think is suitable to sit in one of these seats whether theyve paid for it or not. They can take up the issue of a refund with the airline later, but fact is when they book the seat they are asked questions as to their suitability and yes, people do lie. BUT the most important thing is, if something does happen, it is this persons responsibility to open the exit and get people out, and if i think 80 year old annie, or mr bad back cant do it, then they are not sitting there. this may sound harsh but its what ive been trained to do, as the ultimate authority on who sits there will come down to crew.