Online marketers have always made an effort to predict and gauge what online users actually want, and then get them to purchase it.

Figuring this thing out is never so easy. For one thing, individuals do not always end up buying what they like. For example, someone may purchase a sweater for their grandmother even though they may not actually like it and would never buy it again. Similarly, a surfer who rents a movie may actually detest it, but he or she does so because their child likes it.

Among online retailers; pushing people toward other products they might want or need is quite a common practice. Both Netflix and Amazon, two of the best-known practitioners of such targeted upselling, have long recommended movie titles and similar such products to their clientele.

They achieve this by using a technique termed collaborative filtering, basing suggestions on previous purchases of clients and on how they rate a particular product compared to other consumers.