To cite a bit of wisdom from Mexico, when Mexican shoppers fill the stores of American border cities, something is dreadfully wrong with the economy As the editor of El Zocalo, a newspaper in Piedras Negras, a small city on the edge of Texas, puts it, if Mexicans can buy food at cheaper prices in Eagle Pass, where the dollar wears the crown, then “you know that the peso’s value is inflated.” By the same token, peso devaluations spell trouble, and this is true not just for Mexicans who shop across the border but also for American merchants who stake their fortune on sales to them.