I agree with everyone else. Fairness of a trade has nothing to do with whether or not a trade should get vetoed. What seems fair to me might not seem fair to you. I think it's impossible for any type of software to calculate something that's so objective.
Like the others have said, unless you suspect collusion (2 owners cheating to make 1 team better), you have to let EVERY trade through...even if the trade looks lopsided on paper. I've commished several leagues, and I've been lucky enough to be in leagues where owners don't try to cheat. I have never vetoed a trade (yet!
). And it's not because every trade I've passed seemed fair to me. I thought some of the trades were ridiculous, but I knew the owners weren't colluding so I had to pass the trade. All my leagues do trade pass/veto this way and then we have co-commishes decide on trades involving the commish and/or co-commish.
When it's left up to 10-12 owners, too many people veto for the wrong reason. That reason is usually that the owner getting the better end of the trade (on paper) is in their division.