Well, it's not against the rules. Why would it be? It's two entirely different sales, there's no guarantee to successfully complete such a "trade", and anyone else can bid if he wants.
There's no potential ban doing that. You could make a case for a ban if both teams sell their guys well over their value, but at market value there's no reason to ban anyone.
If you want to be sure, just submit the "trade" to a GM before doing it, and see if it's a fair sale.
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