Who bears the liability (warranty) if the sold item is found to be rightfully claimed by another party (mustahaqqa)?

Primary text

The liability rests upon the mortgagor, not the appointed trustee, provided the trustee informed the buyer that he was acting as an agent. This is the established doctrine of Al-Shafi'i. This applies to every agent who sells the property of another. If the price was paid to the mortgagee and the item is later found to be rightfully claimed by another party, the buyer returns to the mortgagee. This is the position of Al-Shafi'i. The basis is that the actual asset of the buyer's property went to the mortgagee unjustly, thus his recourse is against the mortgagee, as if he had received the price directly from him.