Final answer:
When a seller lets a counteroffer expire, they are effectively rejecting it. No contract is formed on the expired terms, and new negotiations must be initiated for a future transaction.
Step-by-step explanation:
When a seller receives a counteroffer and lets it expire, the seller is effectively rejecting the offer. In the context of contract law, a counteroffer functions as a new offer and nullifies the original offer. If the seller does not respond to the counteroffer within the time frame specified, the counteroffer is considered to have been declined, and the possibility of forming a binding contract on those terms ends. Therefore, the seller and prospective buyer would need to start negotiations anew if they wish to attempt another transaction.