Naradasmriti m2.22

m2.22

arthinā saṃniyukto vā pratyarthiprahito 'pi vā /
yo yasyārthe vivadate tayor jayaparājayau //

If one deputed by the claimant, or chosen as his representative by the defendant, speaks for his client in court, the victory or defeat concerns the party (himself and not the representative).