What you describe is not what actually happens. What actually happens is that your behavior (in store or not) is permanently observed all the time and ads are

What you describe is not what actually happens. What actually happens is that your behavior (in store or not) is permanently observed all the time and ads are served whether you want it or not. Imagine if in all shops, always you'd get jumped on by attendant trying to sell you things. And sometimes shop attendant would appear out of the blue. What you're describing you can have today - just convince user to make account in your shop and give you permission to send offers. You can chase him any time you want.