What is the ruling on a woman exchanging a good quality type of flour for a medium quality type with her neighbor in small quantities (one kilogram)?

It is impermissible to sell usurious flour for the same type, whether with a surplus or on credit. It is permissible to sell flour for flour by measure if they are equal in fineness. If they differ in fineness, it is not valid. If the type of flour differs, the sale is valid hand-to-hand. It is not permissible to exchange good quality flour for lesser quality flour with a surplus, but it is permissible to sell it for it in equal measure (measure for measure).