I know lone star is being annoying with his constant posts, but since this is a good forum for commissioners to learn, I'm going to give my take on the substance of his post:
Scenario 1: Team A trades players to Team B and they agree to split any earnings
This is 100% not allowed, and in my opinion, is something that you should not allow to happen even if you don't explicitly have a rule against it.
Scenario 2: Team C trades star players to Team D, but it is for what the league has determined as fair-market value. There is no agreement to split earnings, but Team C wants to trade to Team D because he dislikes the other owners in the league and wants to make things tougher for them.
As long as Team C is making a good faith effort to improve his own team in the process, I have no issue with this. Preferring to trade with certain owners over others is not collusion, whether it's because you have bad personal relationships with the other owners, or you want to avoid trading to teams ahead of you in the standings, or because you just hate the way other teams approach negotiations (this is a reason why one owner in my league has seen a lack of trades in recent years, he always tries to get too much off other owners and it is a headache to deal with him).
Scenario 3: Team E agrees to not enter into trade talks that Team F is involved in, because Teams E and F have a close personal bond. Likewise, Team F agrees to not enter into trade talks if Team E is involved, but Team G wants to hear bids from all interested teams.
This is the same as Scenario 2, really - there is no rule that you must negotiate with any team that wants to negotiate with you, just that in any given trade, you must be trying to improve your own team.
Scenario 4: Team H agrees to trade a certain package of draft picks to Team I, if Team I beats Team H in their matchup that week. The trade would still be for fair-market-value though. Also assume that teams have been able to make low-stakes bets like this in the past, but this particular instance definitely raises the stakes. No rule against bets though.
This one is a bit of a gray area, in my opinion. I don't really have a problem with this in principle; I certainly have delayed trading with an owner because I'm playing them in the given week. That said, if someone submitted a trade that was conditional, as in, "This trade only goes through if I lose this week," I would tell the person, "I will either approve this trade to take effect immediately, or you should wait and re-submit it after this week's games." I'm a firm believer that when a trade is submitted to the commissioner, it takes effect immediately (unless some of the players involved have already had their game for the week).