If a seller counters a low offer but then accepts a full-price offer before the counter is signed, what is the seller's right?

The seller has the right to revoke the counteroffer if it has not yet been accepted. In real estate transactions, a counteroffer essentially nullifies the original offer and creates a new offer that the other party must accept. Until the counteroffer is formally accepted, the seller retains the ability to change their mind and accept another offer, such as a full-price offer. Once the counteroffer is accepted by the buyer, it becomes a binding contract, and the seller can no longer accept other offers without breaching that contract. Therefore, if the seller receives a more favorable full-price offer before the counteroffer is accepted, they are within their rights to revoke the counter that remains in negotiation.