Final answer:
If a seller receives and lets a counter offer expire, they have rejected that counter offer. The seller must make a new offer or ask for another counter offer to continue negotiations, as no binding agreement exists.
Step-by-step explanation:
When a seller receives a counter offer and lets it expire, the seller has effectively rejected that counter offer. In the context of contract law, a counter offer constitutes a rejection of the original offer and simultaneously presents a new offer.
The expiration of the counter offer without acceptance by the seller means that no binding agreement has been reached. If the seller wishes to restart negotiations, they would typically need to present a new offer or invite the original buyer to make another counter offer.