Trust people from Sporting? No one is trying to convince you of anything. I hope he doesn´t leave us. I want to see him play for us in the Champions League. I did a factual description of Carvalho´s caractheristics and how the season went. No one is trying to convince you if he´s worth 45 million euros. A player is worth what the clubs accept to offer. Hypothetically if United think he is worth 45, it´s their judgement. Would i pay that for him? Perhaps not. But in the long run, if he evolves well, a hefty fee may end up being a reasonable price (I.e Ronaldo to Madrid). The only players who can be deemed expensive are the one who don´t produce on the pitch.
About the competitive level argument. I don´t agree with that reasoning at all. Plenty of world class players have come from our league. Why is it that you have to prove yourself in a more competitive enviroment to prove anything? When a player is good (like Falcão, Rodriguez, Matic, Moutinho) you can play anywhere and against the best. Carvalho trajectory is very similiar to Matic. Why can´t he replicate his success? Just because he comes from the portuguese league? Does it matter? That kind of reasoning makes clubs like United miss on top talents. Wasn´t Feillaini premier league proven? Did it matter when he flopped last year? Where did Matic come from? Which one do you think is the best player?
You can take my words with a pinch of salt but Carvalho is the best talent to come from our academy since the Ronaldo days. Will he evolve and have a good internacional career? I don´t know and neither do you. Our academies track record speaks for it self. One of the best in Europe. Does it justify Carvalho price tag? No. Is he worth 45 million? I don´t know because i can´t predict the future. What i can say is that clauses are standart procedure at our club. Doesn´t mean the player is worth that (Ryan Gauld scottish kid who signed for us has a 60 million clause). If United wants to pay that value it´s up to the club. We have the right to sell him for the price we deem right and are in a good position negotiation wise because of the long term contract and champions league money.