All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The basic principle is that what is in the possession of man belongs to him and he may freely deal with it in selling and buying.
When buying a land from someone, it is not necessary to inquire whether or not it was stolen. However, if the buyer knows that the land which he intends to buy is an inheritance and not a property that is exclusively owned by the seller, then it is not valid to buy it except with the consent of the heirs, as it is known, because the consent of the seller is one of the conditions of the validity of a trade.
However, since people nowadays often consume the rights of one another in inheritance and deprive some other heirs, then he should not buy that land from the seller until he investigates and confirms the consent of the other heirs about the sale, and that the seller did not transgress their rights or intends to sell it without their consent.
Allah knows best.