As the commish in my league I am facing many of the problems you mentioned. Every trade seems to be a hot topic and a few managers basically don't see anything as fair. Anyway, we currently have a majority of voting managers to turn down a trade. There are 20 managers in the league, but not all vote all the time, so we base the majority only out of the total amount of votes.
However, there's a new website that is going to be up and running for next season that I think I'm going to give a shot. http://www.flbtradereview.com
. I emailed the guy running it and he said he has a committee of fantasy baseball gurus who will evaluate every trade submitted to them and respond with a scale of -5 to +5 in favor of one team or the other with a rationale. This service should take out any bias individual members of my league has regarding any specific trade, so that alone will make that service valuable.