Am I sinful towards the one to whom I sold the apartment after its original owner reclaimed it?

The seller might not be culpable if she was unaware of the lawsuit and did not intentionally deceive the buyer. However, she is obligated to return his money to him as long as the apartment is rightfully owned by someone else. She can then claim reimbursement from the first seller for the price she paid. If the sold item turns out to be rightfully owned by another, the buyer can demand the price back from the seller. If a man buys a house and sells it to another, who then builds on it, and the house is subsequently found to be rightfully owned by someone else, the second buyer can claim the price and the value of the construction from his seller. The seller, however, can only claim the original price.