One hour later they showed up on Amazon ads on her Facebook account. Very dodgy.
Like I said, I've definitely observed this phenomenon before. I've also observed that it's likely confirmation bias: I don't remember all the OTHER things Facebook advertises to me. The only reason that ad for the coffee machine jumps out at me is because I was just talking about it, but who knows how many times it showed up on my feed and I just glossed over it because I tend to gloss over ads?
Posts like this come up quite often, and I definitely think it's dodgy and suspicious, but ultimately, I think it's just clever marketing tactics by Facebook to determine what to advertise to you.
It's probably some combination of your IP, cookies, location, account relationships, credit cards, etc etc. There's a lot of pretty simple data they can use to make the decision to show her Ads on Facebook's Ad platform.
[edit:] This may be considered as dodgy. In Germany it is forbidden to use the lookalike audience feature of FB and companies are fined if they admit using it.
1. Amazon passed your [IP address + SKU browsed] to facebook ad platform. And facebook knows from there on.
2. Facebook snoops on your audio and its ad platform pulled SKU from amazon.
3. You have various extensions on your browser which can "read all websites data you visit" - which have sold your browse information with IP to facebook.
Third is most likely.
+ I have noticed - "somehow" my facebook learns what I watch in youtube and vice-versa. Only way this could happen is via one of my "trusted" browser extension!
Looks like youtube doesn't talk to Facebook directly. It does talk to doubleclick though. I recommend installing uMatrix to manage loading 3rd party resources.
Clear all cookies between browser sessions.
I assume its due to the fact your amazon has been linked to her facebook account at one point or another as you were logged in to both at some point.
I mean, we're talking basic product advertisement from the largest store in the world...