Final answer:
The principal concern of the firm's customers in the product market is obtaining reliable products at the lowest possible price.
Step-by-step explanation:
The principal concern of the firm's customers, who are stakeholders in the product market, is obtaining reliable products at the lowest possible price. Customers in the product market are interested in getting good value for their money and are often price-sensitive. They want to purchase products that meet their needs and expectations while minimizing their expenses.