All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
It is permissible for whoever owns something to sell it at a price that pleases him. It is not permissible for you to cheat the owner of the land by buying through someone from his family in order to get the piece of land with a cheaper price because this is deceiving and cheating, and both are forbidden according to the consensus of the scholars .
In principle, the prices are not fixed in Islamic law, and the people are allowed to buy and sell and no one should interfere in their dealings by determining the price or a given margin of profit, as Allaah Says (what means): {O you who have believed, do not consume one another’s wealth unjustly but only [in lawful] business by mutual consent.}[Quran 4:29] In the above verse, trade is only restricted to the consent between the two parties. For more benefit, refer to Fatwa 92029.
Finally, we advise you to seek the help of the pious and righteous people in advising this man to be merciful in selling, and if he does not agree, then you may buy from someone else as you are not permitted to cheat and deceive him.
Allaah Knows best.