What is the consequence if the seller in a concession sale repays the difference that allows the sale to be confirmed up to the full value?

Primary text

If the seller provides another ten (to cover the value difference when the item was sold for ten instead of thirty, and the buyer paid fifteen), according to the first view, the sale is confirmed for eight-ninths of the item in exchange for eight-ninths of the price. According to the second view, the buyer takes half plus four-ninths of the item for the entire price, returning one-ninth.