If agent shopping takes off in a big way it will be another shift in retail over a long arc of "format" changes that have defined the past 125 years of retail. While early customers might focus on the cheapest or "meets my notion of specs without offering alternatives" (eg sales) history has shown that format changes do not necessarily lead to just lower, sales-free, ad-free, transactions. Just a different mode of buying and selling. Need an example? Remember when your favorite online…