when looking at the players, click up their stats and check them. ive found 3 star players with 5 or 6 star for the expertise i need (def for defenders or att for strikers), but their other stat is much lower, so bringing their overall rating down greatly.
quite often these are much better than more even players of the same lvl (my leagues top assist player last year was my lvl 4 amr, when most my team were lvl 5, because his attack skills were through the roof, he just couldnt defend!) also, these players are quite often much cheaper per season than those of better skills, so make them great buys if you are working on a tight budget