Hi,
I've been playing T11 for a while and reading this forum every day, so I wanted to share a few of my insights with you.
1. First of all, this game has hidden attributes, just like Football Manager, Championship Manager and others.
that means you can never tell what kind of player you'll get until you get him. he can be a fantastic trainer but poor performer, he can be a great performer and lousy trainer, and he can be an aggressive player that gets a lot of yellow cards (and sometimes spits..).
The theory says that the higher priced he is, the better trainer/player he will be. that is not always the case, I've had quite a few very expensive players who were awful players or crappy trainers.
2. The star quality of the player doesn't necessarily represent the actual quality of the player, and the performance he will give.
That means that a 5 star/ 6 star player can be a ****ty player who keeps producing 4-5-6 ratings and cost you games, while a 4 star player gets 7-8-9 rating and be a solid performer. In my experience, players that keep getting 4-5-6 rating never get better and only seldom get a 7-8 game, I have tried benching them, hard training them, renewing their contract or even changing their name and nationality, nothing worked, so my advice to you is to get rid of them, and keep the solid 4 star players as long as they play well.
3. finally, and this is just a theory of mine, I think that there are cases that some players will play great and still get only 6-7 ratings. You can see that happening when you see them score, assist or block goals and still get low rating for no real reason. I think it also has something to do with the hidden attributes and a calculation the game engine makes when calculating their star quality and their performance, and then compares it to other, lower quality players that played well.
there a few more things that I can think of but I don't want you to get tired reading.... :-)
Hope this helps and I'll be happy to get some feedback.
P.S.
I'd like to add that since Nordeus introduced Mourinho as a manager, I have a pretty strong suspicion that one of the key attributes in the game is the player's speed skills, just check the speed of Mourinho's players...