What is the ruling on a merchant who sells adulterated goods, and a witness who testifies that they are sound?

Cheating in sales is forbidden, and some scholars have considered it one of the major sins. Many texts have been narrated prohibiting cheating and threatening punishment for it, among them the saying of the Prophet, peace and blessings be upon him: "Whoever cheats us is not of us," and his saying: "Whoever sells a defective item without disclosing its defect, he remains subject to the wrath of Allah, or the angels continue to curse him." Whoever knows about cheating must disclose it; if he remains silent, he becomes a partner to the seller in sin.