Very, very impressive, if (intentionally?) a little vague on how you got to 1m accuracy given you WiFi only gives you 3m.

I guess you must use the constraints on the directions a person can walk imposed by the shelves and other structures to give you orientation of the accelerometers. Which in turn means the person doing the ground truth mapping must walk down every aisle, and into every gap. That's not so difficult if your staff are doing it, but I bet you have trouble training the store staff gathering that data to do it well.

Best of British.