What is the ruling of the Sharia on a man who refrains from informing his relative of the true price of his land so that he himself can buy it at a low price?

It is not obligatory to advise the seller of the true price of his merchandise unless he requests it, based on the hadith: "If he seeks your advice, then advise him." However, if the seller is ignorant of the value of the merchandise, is poor at bargaining, and entrusts the buyer, then the buyer must advise him, and it is not permissible for him to cheat or defraud him.