Final answer:
The sales associate should inform the customer that the last pair has been sold and suggest alternative options or offer to order a new pair.
Step-by-step explanation:
In this situation, the sales associate should inform the customer that the last pair of high-definition binoculars has been sold. They can suggest alternative options such as other brands or models of binoculars that may still be available. Additionally, the sales associate can offer to order a new pair of high-definition binoculars for the customer, either for them to pick up later or for delivery to their preferred address.