I am not a big fan of this situation. I feel like collusion with "yourself" is inevitable. It may not take the form of you making a bad trade to yourself(in fact you shouldn't trade with yourself at all) But it will effect waivers/pickups/draft everything really as well.
If you are asked to fill a league with a second team, that is ok, but needs to be tread upon very carefully.
If a person attempts to mislead you about having two teams(having 2 different yahoo id's etc) imho whether they have cheated or not yet, the only reason you would do this is to cheat, so simply the act of doing so is a removal from the league offense.
However you need to be sure about it being a double owner. IP address is a good start, even if its two people playing from the same location these people need to be scrutinized more carefully than others. This isn't to say that two people playing from the same location are cheaters, but that the propensity for collusive behavior to occur between 2 people who know each other and 10 people who don't, is MUCH higher than the chances of it happening with 12 random people. We had plenty of examples last year of "two buddies" or "father and son" who were making semi-collusive if not _outright_ collusive trades that would never be made between to strangers.
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