To execute an unfair trade with the trade logic on, trade many times. You can trade a 70 overall player for a 71 or 72. Once that you have that player, trade them for a higher overall player. Once you work that player up to someone who is about 90, it is as if you traded your 70 overall player for the 90 overall player. Note: If this is done a lot, teams will be more unlikely to trade for good players.