представлять интересы(act for somebody | act on behalf of somebody: to be employed to deal with somebody’s affairs for them, for example by representing them in court. OALD Alexander Demidov)
действовать в собственных интересах(Accountability: An attorney is accountable to you and must act in your best interests. Joint account holders are not accountable to other joint account holders and may act for their own benefit. (rbcroyalbank.com)ART Vancouver)