In last decade and even longer, Manchester United was completely a newbie on transfer market by purchasing players with super overvalued and expensive transfer costs. It is more painful as later they did not use those expensive players well enough and made it like doubled failures.
All clubs can make transfer mistakes that barely happen while with Manchester United, they have been doing this in many latest seasons. Hence, it is no longer mistakes but more likely severe systematic problem from their club strategies for development and necessary actions on transfer market.
Making transfer mistakes can happen to all clubs. But the question is how they can fix the mistakes so that they will not happen in the future. It is not easy to admit mistakes especially if it is a lot of money. It takes courage to say about the mistake and solve how to fix the mistake.
They can buy expensive players if they can manage it to perform with other players. Playing as a team is more about how to unite them in one command and that is not easy.