You could do a test. Get someone to take your (locked) smartphone into a well-known dealership for something you aren't ordinarily interested in. Blind test, you don't know where they took the phone. Google tracks the physical location of your phone (don't know if it's possible to completely opt out of that)... trivial to match that to "dealership X" given that Google Maps already knows about those. If in the blind test you can tell your friend where they took the phone based on increased ad activity, then there's proof.

A day after I started using an Android device: I cycled to work, and my phone gives an alert and asks me to rate X. WTF? Oh right, I cycled by X on the way. I immediately turned off what I could; no more popups like that but do I really think Google doesn't track my location any more?