So, after reading this thread and a few others from other sites I decided to pick this up. I'm not much of a baseball fan, but this game rocks. RTTS is very entertaining. It's worlds better than any other sport title single player career mode.
I'm not sure if it's common knowledge but I found a way to keep from getting traded in RTTS. Save and re-load right before you get traded. Navigate to User Settings>Gameplay>General. Then scroll down to "Injuries" and set it to "Manual". After that navigate to "Disabled List" and then "Manage Injuries". Scroll down to your RTTS player and give them a minor short term injury(3-5 days). Viola, no trade. Remember to turn injuries back on after you're past the trade.