There's one way to be almost certain that someone is autoblocking, a simple way that players can easily do, no it isn't doing retarded easy to see feints and then flipping out when he magically manages to somehow see the slow feint and block accordingly, it is instead holding an attack, watching him block, then blocking and cancelling your hold, if his block instantly turns into a downblock there is a large chance he is autoblocking, and even then only if it always happens and if he never makes any accidental wrong blocks.