Not sure why they would be checking carryon size. At my terminal that is all up to the airline. As long as the bag will fit though the x-ray, we'll screen it. Now I will say this, if one person is carrying a cartload of huge suitcases, then we might say something if the airline doesn't catch it since that one will certainly be an issue when the passeger gets to the gate. But other than that, if a person has an extra bag over and above the one carryon + one personal item or the bag is a little bigger than a normal carry-on, doesn't bother me.