Do not play in leagues with league-wide vetos. It is the stupidest thing in all of fantasy football. Every manager will vote for their own benefit, not what they think is fair or not.
The ONLY time a veto should be allowed, and only be commissioner, is when the trade is collusion. I.e. 2 players working to the benefit of one player at the detriment of the other. And this is very hard to prove. AN example would be like someone giving up like a 1st round draft pick for a 2nd round draft pick in dynasty or something. Or like giving up a starting QB for a 3rd string QB.
The concept of a fair trade from a subjective nature shouldn’t even really come too much into play. One sided trades shouldn’t even result in a veto tbh.