I think the most WTF sale was Llorente.
No it wasn't.
Fans make up theoretical value's of players in their head and than act as if a player is worth that amount, not understanding that the market itself - and only the market - determines the value of a player, which includes the salary of a player. And in the case of Llorente - because of his way over the top salary - the market determined his value to be zero.
Marotta had two options: Keep Llorente and his salary of 8 mln before tax or give him away for free, saving 8 mln euros a year. There were no other options, no manager in the world could have gotten a different deal, it's not like Marotta didn't try to get more for weeks. It was either or in the end. Everything else was and remains wishful thinking.