Final answer:
The least sustainable competitive advantage for a footwear store would be lower price, as competitors can always match or undercut the price.
Step-by-step explanation:
The least sustainable competitive advantage among the given options for a footwear store would be lower price. While offering lower prices may attract customers in the short term, it is not a sustainable advantage because competitors can always match or undercut the price. This can lead to reduced profits and potentially drive the business out of business.
On the other hand, shared systems with vendors, convenient store location, knowledgeable employee force, and helpful sales force can all contribute to a store's sustainable competitive advantage. These factors can differentiate a store from its competitors and create value for customers.