Is it permissible for my husband to tell the buyer that the price of the camel is 30,0, while it is 20,0, without either party knowing?

If a man buys a camel at one price and sells it at a higher price, it is permissible, whether the buyer knows the original purchase price or not. It is also permissible for him to receive a commission from the seller, the buyer, or both, according to custom, provided that the price is known to both parties.

However, if he informs the buyer of a higher price than what the seller informed him of, and he undertakes the sale as an agent for one or both of them, then this is not permissible, due to the presence of falsehood, taking money unjustly, and causing dispute.