If two parties make a transaction that entailed a Torah violation, such as if the goods were delivered on Shabbat, can the buyer retract the sale and demand a refund? If, for example, the goods were delivered on Shabbat and the buyer then realized that such a transaction cannot possibly yield profitable results, as it entailed Shabbat desecration, can he retroactively rescind his consent to the sale and demand a refund?
The Shulhan Aruch addresses this question in Hoshen Mishpat (235:28) and rules that the sale in such a case remains binding despite the Torah violation involved. Even though the parties are liable to punishment for having transgressed Torah law, the transaction itself is legally binding and neither party can retroactively rescind his consent.
Earlier in Hoshen Mishpat (208:1), the Shulhan Aruch addresses a similar situation, where the parties agree that the buyer will render payment a year after the transaction at a certain percentage of interest. Paying or receiving interest constitutes a grave Torah prohibition, and thus this agreement entails a clear violation of Halacha. Nevertheless, the Shulhan Aruch rules, the sale remains legally binding and neither party can retract his consent to the transaction. Of course, the buyer is not required to pay the interest; in fact, he is forbidden from doing so by Torah law. The transaction itself, however, is legally binding, and therefore neither the buyer nor the seller can demand that the sale be voided on account of the forbidden nature of their agreement.
Summary: If a transaction entailed a Torah violation, such as if the goods were delivered on Shabbat or if the arrangement entailed the payment of interest, the sale is binding despite the prohibition involved, and neither party can retroactively void the sale.
See the book- "Pure Money" by Dayan Cohen, pages 97-98.
