Pretty good deal TBH.
Sassuolo wasn't going to buy Marrone's remaining half, and I doubt anyone else would pay 4mln for Peluso.
The only thing left is to sell Marrone for some 8-10mln or include him in some deal for that value.
If I failed to mention his "usual" wrong passes, you completely failed to mention 99% of his other passes, going as far as describing him "the worst passer" when it clearly wasn't the case.