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.
If this is done a lot, teams will be more unlikely to trade for good players.
If you need more skill and less depth on your team, you may want
to trade two of your average players for a good player. If you
trade two players in the 80 to 85 range, you can receive a player
in the 90s and a player in the 70s in return.
Go to Free Agency and sign on a player with about a 60 overall
average. The game will state that the team already has a maximum
amount of players. Sign off the player that you want. Then, go to
the Free Agency and sign on the player you want onto your team.
You can now have their players without trading.