I've always thought trading would be a ridiculous proposition in this game due to what others have already mentioned with all the cheating that would happen, but with certain rules, it could make sense.
For instance:
- Only players with TSP's over 80 (so no scrubs are ever involved in trades)
- TSP's of players being traded must be within 5 points
- Ages of players being traded must be under 32 and within 3 years of each other
- You can do a two for one trade, but the two players must add up to 1.5X the TSP of the one player, and they also still must have TSP over 80, so you'd be able to trade two 80 TSP players for a 107 TSP player - it would be a sacrifice to do so, but to get a really awesome player for your team, you would still do it.