If Facebook indeed does this, it should be fairly easy to trigger by repeatedly mentioning some kind of product in front of a running Facebook app. If not, it's a "can't reproduce" for me.
We mentioned Target, including a request for upcoming sales and target credit cards, Advil, Colgate, Liquid Plumber, Scott toilet paper, Wells Fargo (though we need to rule that out bc my daughter's been googling them re DAPL), Citibank, Marriott, Red Lobster, and an imaginary pending trip to Maine.
I will report back what we see.
edit: none of these do we use or see ads for.