"It is possible that facebook has access to a stream of Target purchases" ...
It's not possible, it's simply true. In fact, this feature of the facebook ad platform is available to any advertiser on Facebook/Instagram/etc, whether you have $100 to spend or $100M.
You simply upload your customer's purchases to Facebook with data such as zip code, email, etc etc which Facebook then uses to optimize your advertising budget and find more customers similar to the ones you already have (the feature is called look-alike audiences).
It's not possible, it's simply true. In fact, this feature of the facebook ad platform is available to any advertiser on Facebook/Instagram/etc, whether you have $100 to spend or $100M.
You simply upload your customer's purchases to Facebook with data such as zip code, email, etc etc which Facebook then uses to optimize your advertising budget and find more customers similar to the ones you already have (the feature is called look-alike audiences).