Bollocks to it, mods were saying earlier they were removing posts related to it, but have been visiting here all night and didn;t remove the earlier one. So here you go, its getting updated soon anyway.
It requires you to have an amount of money to cover loyalty fees, signing on and agent fees. But the transfer fee you pay will be 0. It cannot be used to sign 'any' player, only those that are interested in joining your club, so it isn't going to work for Messi or Ronaldo.
1, Find the player you want to buy and select what you want to pay, just make them an offer they cannot refuse. Then press 'Suggest Terms' and the response at the top should say that the offer is acceptable. Then click 'Make Offer'.
2, You then wait for the contract negotiation, as you should know, this can take a day or two. When it does, just click 'Walk Away'.
3, Immediately go back to the player again, and change the transfer offer to 0 and once again click 'Suggest Terms', they should now find the 0 offer as acceptable. Then click 'Make Offer'.
4, Wait for the contract screen to come up again and they have accepted your 0 offer and you can discuss terms with the player, resulting in you signing the player for 0.
Credit to Mersk for posting it here earlier.