One that is beyond duality remains unaffected by abuse or pleasure and lacks all other contingent attributes that may distract from enlightenment. The guru who is free from duality is a satguru.
The satguru is aware of the absolute Truth, which is comprised of all fathomable truths. He is the preacher of all fundamental secrets and teacher of true Self-realization. A satguru is one who liberates us from suffering (through his/her example) and encourages direct contact with the Self.