I came across this cheat when in the comparison menu, select one of your RESERVE team players, it must be a reservee, or just move the first team player you wish to get rid of to the reserve team.
Then select in the other box, the player that you want (this can be anyone of any price).
Then by pressing the square button you request a player swap, this now brings up the negotiations screen, stay where you are and the team that you are negotiating with should move over to you.
Hence you agree the swap as well as they pay you a nice sum depening on the price of the player they swap ( swaping your rubbish platers for the most expensive on the game, such as Totti and Henry gets you about £8m+ ).
NOTE: Alhtough in most cases, the other team will normally always move their negotiations all the way to you, some times you may have to move yourself, end up having to pay a few £k for the player ( but whats a few £k for the players you can get!!! ).
You can repeat this as many times as you wish to get your dream team, but beware because you have to foot the bill for wages, so buy carefully if you want to stay above the red.
I hope this cheat helps because I can't find any other good cheats for this game anywhere!.