The value of a player is that which other clubs are willing to pay for him.
So when it looks likes a deal is done for Matteo Guendouzi to Marseille for £10million, that is his value.
It doesn’t matter if some fan boy moans we are underselling. £10million is his value.
If Guendouzi was as good as what some claim, surely teams across Europe would be queuing up to sign him for £10million? But they are not.
And if teams were queuing up for him, that would then naturally push the price up as teams competed for his signature.
But no other team other than Marseille seems to be interested. And they only want to do a deal for £10million. So that is his price.
If you are sitting criticising Arsenal for the deal, just ask yourself why no one else is in for him. And the answer to that is why Arsenal are selling him.