You'll find that stars don't mean a whole lot.

Think of them like combine numbers from the NFL Draft scouting reports. In case you (or other reading this) aren't familiar with what that is, before the NFL Draft, players are tested by position as well as all their measurables taken.
Height/Weight, various times in drills, bench press reps, and some position specific exercises.

Player A might greatly out perform Player B, in measurables, but on the field, for one reason or another, Player B turns into a solid player, while Player A is out of the league in 2 years.

So when you get a player whose young and consistently gets 7s and 8s, keep him until he stops getting those ratings, even if he is only 2 or 3 stars. Some players just know how to get the job done, while others don't.

Perfect example, on my friend's team when she was level 4, she hit the jackpot on the transfer market and got a striker who had really nice stats for his old team and was only 2 points away from scout with a heavy skew to attack. After the transfer was complete, we noticed he came from a level 8 team, so he would have seen him as a 1 star player, yet he was still scoring goals for this guy in level 8! His first season for her he got over 40 goals and 40 assists, now at level 7 with only a few more points, he's still scoring!

Meanwhile on my team, I keep getting 18yr old fast training strikers at Day 1 of the season who turn out to be bums, my last one got 2 goals in 17 matches before I moved on.

My team this season started our rather poor, losing to lower teams, but I switched out my MCs and got a new striker and my team completely turned around.

So take the stars with a grain of salt, judge them by their performance on the field.