Some months ago, Harry Saltzman and his wife, Barrett Cobb, were planning one of their regular trips to Europe. Saltzman, a retired music professor who lives in Manhattan, is a foodie, and he was looking forward to the Spanish segment of the itinerary. A week before they left, he received an e-mail message from La Tienda, an online store he had patronized. The subject heading was "Do you want to visit your ham?"
Saltzman originally came across La Tienda while...