Sometimes referred to as "organic" recommendations, passive delivery presents the recommendation in the natural context of the rest
of the E-commerce application. Examples of passive recommendation include displaying recommendations for products related to
the current product (Amazon.com's Customers Who Bought feature), displaying recommendations for products related to the topic of
a text article (CDNOW’s Artist Picks) and displaying recommendations in the context of exploration (Drugstore.com's Advisors).
Passive recommendation has the advantage of reaching the customer at the time when the customer is already receptive to the idea.
Indeed, E-commerce uses passive recommendation as part of the ordering process, suggesting upgraded shipping options, for
example, at the time when the customer is completing a purchase (where it is much more effective than asking about shipping on a
link off the home page). A possible disadvantage of passive recommendations is that customers may not actively notice them, but we
are not aware of any research that suggests that noticing recommendations explicitly makes them more effective than having them as
part of the overall experience.