In Catholicism, one can discern between a robber Council and a true Ecumenical Council: the Pope gives his ratification of one and not the other. Therefore we know that the correct Council was adopted.
In Eastern Orthodoxy, on what basis is one Council accepted (an orthodox Council) and another rejected (a 'robber' Council)—which doesn't strip an Ecumenical Council of its binding authority to teach and inform (i.e. place judgement of Councils on something below the authority of an Ecumenical Council)?1
Thanks in advance.
1 Catholicism rejects the notion that an Ecumenical Council is above the authority of the Pope, which is called the Conciliarist heresy.