All items are scanned on the way out anyway - you should be able to get an idea when an item is low on stock from that alone, no? Sure there will still be things like people in the store that haven't checked out yet, but...
When an item comes in from a truck it either goes directly onto the sales floor, into overstock (a high shelf above the other items), or into the backroom. People put things back in random places, stuff get destroyed (think of dropping a can on the ground), stuff get stollen, cashiers make a mistake, people make a mistake in self checkout, probably other stuff I am missing. It is a store, things are chaotic.
Let's take the journey of some cans of Goya black beans. 12 come in on a truck. The shelf capacity for them is 4. The person unloading the truck takes beans to the sales-floor, puts 4 on the shelf, puts 4 into overstock puts 4 into the backroom. Joe walks in takes a can, drops it and it bends. Jane comes along takes a can, continues shopping, the changes her mind and leaves it somewhere in the cereal aisle. Janet comes along and takes a can, takes it to self checkout but forgets to scan it. Jacob comes along takes a can, takes it to the checkout, and 1 can is subtracted from inventory. Inventory shows 11 cans, but there are actually 0 cans out on the sales floor. And I haven't even gotten into stuff being misplaced in the backroom ect.
I work (transitively) for a very large grocery retailer that rhymes with "Broger". Live inventory data is mostly junk -- it's sorta reliable in broad strokes, but you can't rely on it for determining out of stock events. There'd be all sorts of false positives and false negatives.
Like 20 years ago I worked at a grocery store when they were introducing "live inventory". Goods got scanned when unloaded from truck, and of course the register.
One day a customer complained we had no more washing powder of the most popular brand. Boss came, said they just got some the previous day, checked the inventory system and saw there should be three "trays" left, each with 12x packs of 1.2kg. He went to check the back, nothing there.
After a bit more searching he had a hunch, and checked the cameras. Sure enough, someone had loaded the three trays into a duffel bag earlier that morning and walked right out.
So yeah, even with all the normal human elements in the logistical chain, kinda hard to keep track of blatant theft.
As someone who has had to clean and analyze inventory data, I can't agree with you enough.
In every company I've worked or consulted for, inventory reconciliation is always an ongoing headache for every business with a retail component. It is unbelievable how much waste and loss comes about from this.
Are their any companies achieving some level of automation? I would be very interested in learning more.
Theft, misplaced items, etc. Employee grabs it to use for the store, damaged items, etc etc.
With only using in-out the inventory system thinks there are plenty to sell and won't reorder, but if it's wrong the shelf is empty and can't be reordered. There are posts from Walmart people online complaining about this exact problem.
Affects me as a customer, hit their website says they have 10 in stock for pickup today, drive over and the shelf is bare. Ask, they say the inventory is probably wrong, check another store because they can't reorder.
Now they are missing x items + y lost sales. That's why place do inventory.
What am I missing?