In a way, i've two man utd saves playing at the minute one with and one without Hernandez, He isn't good enough for first time sadly, but should of asked for more, I sold him for ?25m, apart from that it's pretty good.
Mistake as in you got little money for him? Not really. Could've maybe squeezed off a little bit more, but ?20 ain't low.
Mistake as in selling a potentially useful player? Depends on what role you're playing your striker as. Chicha is still one of the best poachers in game, but in any other striker role (just like in real life) he's not that good, due to his technical abilities.