"Shopping Friends" is a service that analyzes your Amazon buying patterns and matches you with like-minded people.
Maybe it’s a Facebook app. When you join, you give it permission to access your Amazon shopping records, and maybe there are some filters for what kind of people you want to be matched with (e.g. same country versus anywhere in the world). There would need to be a preferences control panel that you can get to somehow to change these filters afterward.
Automatically at periodic intervals (maybe the interval can be configured but probably defaults to once per day), the app offers you a friend suggestion. These are mutual introductions, so if person X is being suggested to you, then you are also being suggested to person X. The introduction includes the reason for the suggestion. For example:
"Shopping Friends has a friend suggestion for you: John Doe in Portland, OR. Suggested because John buys a lot of Apple products." There are two buttons: Invite and Ignore, and a checkbox: "do not suggest any more people like this."
The Invite button just does the normal Facebook invite process, so of course, the other person may decline your friend request.
It might be interesting to have some advanced options; for example, the number of criteria that must match for someone to be recommended. It would default to one, but if you set it to two you might get a suggestion like "Shopping Friends has a friend suggestion for you: John Doe in Portland, OR. Suggested because John buys a lot of Apple products and books about cooking."