Is it permissible to sell a substance mixed with a lower quality substance for the price of the good quality substance?

It is permissible to sell a mixed substance provided its condition is explained to the buyer.

It is not permissible to sell it to someone who is known to defraud and deceive others with it, because that constitutes cooperation in sin and aggression, which is prohibited by the Almighty's saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression."

Selling it without clarifying its condition, and presenting it as pure, is considered deception. The Prophet, peace and blessings be upon him, said: "Whoever deceives is not of us," and "The two parties to a transaction have the option as long as they have not parted. If they are truthful and clarify, blessing will be bestowed upon their transaction. And if they lie and conceal, the blessing of their transaction will be erased."

Truthfulness in selling is obligatory and brings blessings, while deception is forbidden and eradicates blessings.

The trustworthy, truthful Muslim merchant will be "with the prophets, the truthful, the martyrs, and the righteous."