This book https://www.amazon.com/Aisles-Have-Eyes-Retailers-Shopping/d... goes into quite a bit of detail about various techniques retailers use to track customers.

Not Google specific, but some good reading on this topic came out in January - The Aisles Have Eyes: How Retailers Track Your Shopping, Strip Your Privacy, and Define Your Power [0]

[0] https://www.amazon.com/Aisles-Have-Eyes-Retailers-Shopping/d...