i think its stupid for one team to trade a player who has a salary of 40k to be traded to a player of 8k who doesnt have too much upside. same as the nba, the commisioner's office screens the trades if they can go through. likewise if those nba teams do follow the rules.
but trades aren't official, i think must of cheating detection works through other buyer seeing high prices trnasfer which are reported to gm, i see to much effort in checking each trade manually with an gm.
And trading make it possible to cheat a lot, also in your own league don't forget you know then, maybe you get an friendship deal etc. Maybe you trade starplayers for one important game to the other team, or make bets with players.