What is the ruling on selling poor-quality charcoal after mixing it with a good type, provided the customer is informed?

This transaction is a form of Mudarabah (definition) (profit-sharing), with the condition that you receive a known percentage of the profit and bear the entire loss yourself. As for mixing good coal with bad and selling them together, while disclosing their condition to the buyer, it is permissible and not considered cheating, provided that the buyer knows the quantity of the good and bad, and their descriptions. It is permissible to sell this mixture to someone who will not use it to deceive others, but it is not permissible to sell it to someone who is feared or known to use it for deception.