You are welcome to join the quest to find the theory of everything.
I know how to make American style(NFL,NBA,MLB,etc.) player trading work without cheating: restrict trading to within your own league.
I would never ever trade one of my players to sb. else in my league unless I wanted to cheat.
and if you want you can sell a player to team X and then buy your desired player from team x anyway.
Not really, often some other random BB user intercedes and the "trade" process doesn't go smoothly. I think that a trade system that I suggested could coexist with the transfer system and help out BB.