You have two choices. You can either leave all trades upto a league vote with the decision based on the number of botes foror against the proposed move. Or you can have commisioner rules only. There are plusses and minuses to each type of ruling, but it appears that more griping and league splits happen when you are looking for a majority rules vote. Last year lots of complaints coming from lots of leagues. In my leagues, only the commissioner rules on trades and I never turned one down yet. I had to deal with a questionable one that on paper didn't lookquite fair. SoI had both managers explain their rationale to me, and once done the trade was approved without another thought. Good Luck.