@Freakiie: That is completely fine and a different problem. If a player does not develop, well nothing is paid. But to pay little to no cash and only get the player because of offering crazy premiums which can easily be avoided to be paid by an onsale, just does not make sense. If he really develops nicely and you then cash in on higher market value. And that is the biggest difference to the game when compared to real life, as it is pretty clear in the game who will develop well. Therefore, it should be made more difficult to buy players with adding premiums (as future risk is limited in the game).
@turnip/spallo: My post was meant to be as an idea to improve the game and to make it more realistic. It's great how many options and premiums are possible in the transfer market and why not make it a little more realistic? Could be simple maximum limits in the background on premiums related to cash amounts, which is really not hard to add. Or, as I mentioned, one could leave the premiums as is and only add that those are paid if the player is sold within e.g. 2 or 3 years or a certain percentage of that. That way, you align the game to what's happening in reality, which will further enhance the game.
For me the point is, since it is a game and players have a certain outcome regarding their ability (and hence future transfer price), the transfer market should be made much harder, as the game - naturally - misses out on the risk of future development of players.
Also, I don't quite understand the single player/multi-player argument. It's the same game experience and if it is too easy to buy top players by creating revenue through trading, it's no fun to play - single or multi player.