I am quite new to ad targeting field, and have a question while reading blogs about cookie syncing.
Let's assume User123 has never been to Amazon.com and Facebook.com in her entire life, and the scenario is User123 bought a PS4 on Amazon and then visited Facebook.com and saw a couple ads of Xbox, Nintendo Switch, etc(she visited Amazon first and then Facebook).
When visiting Amazon, Amazon generated a Cookie Amazon123 for User123 and then called Facebook to generate Facebook123 to map to Amazon123.
Now after leaving Amazon for Facebook, how does FB know that the one who's visiting is actually Facebook123 instead of considering her as a new user and generates Facebook234? Is it because both Cookies collect other user information (like machine id?) so they can use it to do a matching?
Or if the whole assumption is wrong, what is the correct work flow?
Your hypothetical situation is a little unique from a standard mapping process because both Amazon and FB have logins which would be used for consumer mapping rather than cookie IDs. But for the sake of this conversation and to keep things simple we can use your hypothetical situation.
When your hypothetical consumer visits Amazon on a browser (not an app) Amazon lays a 3rd party cookie ID into the consumer's browser and calls it Amazon 123. When the same consumer visits Facebook the same process happens and Facebook drops a cookie ID called FB 123 into the consumer's browser. Until the consumer deletes their cookies (most browsers automatically do on a monthly cadence) then every time the consumer visits FB, FB is able to request the cached ID number and figure out that they are speaking to consumer FB123. Once that consumer deletes their cookies FB would not be able to identify that consumers as FB123 unless the consumer logged in.
At this point Amazon and FB don't know that these two cookies are the same consumer unless they ran a cookie match which they would never do because both platforms are walled gardens.