I have never spent a **** load of money on one player... I did buy Milos Krasic - Juventus for my Man Utd side, he played averagely for the 1st 15 games and thought, **** he is going to be a huge flop but then was the best player I have ever bought... payed 18.5 million 3rd season for him...
for my Villareal game I got Thiago (Barca, but went to Deportivo) for 12 million, he was playing very well so was Verane (12 million) both over 7.2's average rating and Verane scored several goals in his 1st 15 games or so...
I am trying to think if I have had a flop of a player, but I cannot recall it, I am just patient with players, giving them time to adjust, settle etc, get used the league, so if I pay 10million for a striker and he only manages to score 8 goals in 20 games, thats pretty normal in my books in comparison to real life (Strikers in Fm dont always have to score a goal a game or more)