Well I would guess that whoever got to the exit row door first would probably be more able bodied then the average person who would sit in an exit row. It ain't gonna be the 400 lb person in the back or the 90 year old in the front.

I have no problems trusting somebody who gets to the door.

Though if I boarded and that row was empty, I would move into it if it offered more room as soon as the door was closed.

With so many airlines charging for exit rows or not allowing passengers to prebook, it's not shocking they go without people in them anymore.