Like a Valverde, who Real wouldn't sell.Right.
But another significant difference is that Casemiro had spent the bulk of his career proving himself at the top level of football, whereas Pahlinha at 27 had spent his career playing in the Portuguese league.
The ideal player is 25-26 years old and has proven himself at a top club for 2-3 years. But then that's quite rare (and costly)... you'll have to assume the risks on age, proven ability, etc.
Big clubs don't sell those types of players, unless its is for an enormous fee. I dont recall the last player at his peak who left one big club for another. Maybe Coutinho to Barca?
Look at the big transfers now - Rice, Caicedo, Enzo, Kane, Bellingham, Gvardiol. All coming to big clubs from lesser teams.
Anyone big club selling now is doing so because they player is either past their best or they have found a better, and often cheaper replacement.
The fact that the Casemiro sale funded the Tchouameni transfer tell you all you need to know about the transfer prowess of Real Madrid and MUFC.