It’s not up to you or other teams to decide what’s fair or not. In my league one guy traded Cooks for Cam day before the season started. Everyone “knew” that the guy getting Cooks was getting a steal. But so far it hasn’t helped or hurt anyone yet. If the two teams agreed to it, let it ride. Is the guy giving up Evans hurting at RB? Why not take a slight downgrade at WR and take a chance on the guy that just got 20 touches for Seattle plus another back that may or may not pan out.
Bottom line, only veto if there’s collusion.