One of the most popular forms of personalization used on eCommerce sites is the “people who bought this, also bought that” recommendation. The assumption is that people have similar tastes and so if other people are buying the same things, so should you. Sometimes, the intention is to ensure that someone who buys an item requiring additional accessories be reminded of all that is needed before checking out their shopping cart.
Some sites use an algorithm to predict which products should be paired with each other. Others simply tag products and bucket them into groups. Now the latter can same time and money, but sometimes leads to some strange recommendations as seen below on the Tiger Direct website.