[Germaniac]

In theory a Commish can cheat - but as it was said before it would become obvious.
Where there may be a chance without getting caught is when you face the Commish in the World Series - I believe he could backup the files and sim for as long as he thinks until the right result appears.

BUT:

I'm in several leagues - and in one I even faced the Commish in the Series - and i haven't come across one I didn't trust 100%, because why put up all that work when you cheat to win the league ?

Oh, one Commish I didn't trust at the end and eventually left the league because of it.
I was talking a blockbuster deal with him, one of my players would have been a FA at the end of the season - and I knew I couldn't afford him as far as his demands where. We had agreed on a 3-for-3 deal, and just before pulling the trigger he backed off, saying that he couldn't afford to re-sign him.
I was - and still am - sure he checked to find out what his contract demand was.

Anyway, basically it's no big deal - you're in a league where you don't trust the Commish for one reason or another ... simply pack your bags and leave. Again, the huge majority of Commish's are 100% trustworthy