Mine is a 12-team standard league. We have a 24-hour trade review period for any trades that are accepted, and if a trade gets 6 vetoes, then it doesn't go through. As commish, I also still retain the option to override and veto any unfair trades on the off-chance that not everyone has a chance to review. I think 6 vetoes is a tad high, but I wouldn't go any lower than 4 for a 12-teamer. Team owners can actually vote "yes" or "no" to the trade, to if there are enough "no" votes (aka, vetoes) then it doesn't pass. Ususally the two people involved in the trade vote yes, and then 1 or 2 others plus myself. Participation is chronically low in my league. However, we did have a case of collusion last year, and the league was with it enough to line up 6 vetoes and can the trade...so it worked just as it's supposed to.