I think that's overengineering. Why not just use weight, like they already do in the self-checkout line? Weigh the shopping cart full of groceries, subtract the

I think that's overengineering. Why not just use weight, like they already do in the self-checkout line? Weigh the shopping cart full of groceries, subtract the weight of the cart itself, and compare to what they're paying for. If it seems wrong, investigate.