In Stores, Secret Bluetooth Surveillance Tracks Your Every Move - The New York Times

This is a good reason to be wary of installing retailer apps on your iPhone, it gives a hook to get all sorts of private information from you that just isn't available in a browser. I also think it should be required that Bluetooth beacons be visible and identified in stores. I think it’s fine to have them, but you should be upfront with your customer and let them know that they are there and specifically let them see where they are.