Fish made this, i mean the war system is exactly what u are looking for.
Set game to forst to 3 wins, for example, bouth upload items in the system, accept if agree and there u have it.
If u ping u loose 1 point.
But what happens if somedy leaves the duel because he dosen't want to loose, and the items get stuck there, until they fight again... That idk how can be fixed.
U guys think of solutions.
Or just duel the old fashion way and take screenahots at all times to support an eventual scam report...