I've always been told never to move the controls from the outside of the aircraft either (...)
Just curious, why would that be? Granted, I don't touch the flimsy trim tab on the rudder and don't bang any control to its stop either, but I always move ailerons, elevator and rudder and have a look at all visible elements. For the DA/DV 20 Katana, the POH even instructs you to check movement of the aileron linkage through a small plexiglass window on the underside of the wing, which would be impossible to do by moving the controls from the inside (unless of course one has such long arms that an airplane isn't really necessary for flying
).