Well, another approach would be to do some controlled experiments: Pick a selection of somewhat-uncommon products. Get some volunteers to set up Facebook accounts on clean computers and phones with no adblockers. Monitor their incoming advertising messages for 2 weeks.
Then randomly assign the products from the first step to the volunteers, give them information about the product on paper and ask them to hold verbal conversations about such such products.
If they start getting adverts that happen to match the subject of those verbal conversations, something is going on.
Then randomly assign the products from the first step to the volunteers, give them information about the product on paper and ask them to hold verbal conversations about such such products.
If they start getting adverts that happen to match the subject of those verbal conversations, something is going on.