While some states have buyer remorse laws, but there are no ‘seller’s remorse’ statutes.
Unless a cancellation option has been written directly into the sales contract signed, the seller cannot typically back out of a purchase agreement.
Of course, a purchase contract can be broken unilaterally by the seller, but expect the buyer to pursue damages if such a tactic is employed.
A purchase contract could also be ‘bought out’ through negotiation, i.e. a payment is made to the buyer to rescind the deal…