One thing that people often forget is TVs / stream boxes and Alexa/google assistants.

Smart TVs all have microphones that are recording (for "voice commands") and the same with the remotes for stream devices (though probably not unless asked because of battery life), also google and Alexa's are constantly always listening. They are simply spyware devices that parse everything you say and hand it to advertisers, insurance, governments, etc...

Phones also suffer from the battery life problem, so jury is still out on whether they listen to you because constantly recording audio would degrade battery life quite a bit (though maybe it is factored in). Phones absolutely do share location data and any phones discovered on the same WiFi network or in the same location if that data was available and from there will share entire search history of devices on the same network (well, that is on the data center end, phones likely just send what devices and for how long they were together). From there it is quite easy to advertised based on search history, unencrypted text data, etc...

For example in OP, OP had likely searched around about cars and checked out manufacturers websites and such before meeting with the parents (unless they were going in completely blind to dealerships), so it would have shared exactly the cars that they were looking at and linked it to the parents for advertising.

Still fucked, ethically wrong and legally grey, but "listening" is a bit of an inefficient way to do it, generally.