But in all seriousness maybe something like base it on a vote of other managers. I mean thats how Yahoo fantasy sports does it, but timing wise i know that can be tough.
Timing wise it doesn't work to have a manager vote. Additionally I don't want owners to be campaigning to vote down or up other managers trades.
This game have enough friction between owners, no reason to add to it.
Or just a rule that their will not be any vetos unless it is found out that a player is undermining the game. Two GM's working together.
Proving collusion is virtually impossible, and it doesn't eliminate lopsided trades where one side is severely taken advantage of.
Vetoing isn't something I will be doing lightly but it is almost certainly going to happen.