Walmart is best checked out in sporting goods while buying ammo or the garden center.
Please, do not check out in sporting goods or the auto center with more than 10 items or so. It's obvious they're not setup for large checkout, yet folks will show up with a cart full wanting to check out. And the employee usually has an impossible-to-complete amount of work to accomplish before end of shift.
Walmart, and I'm sure other stores, has a policy that hourly employees can not confront a suspected shoplifter. It's a fire-able offense. At most, the employee can ask the thief if they need any help...
I think the cost of labor, regulations, healthcare, payroll taxes, legal liability, etc is pretty high these days. I can easily see why they want to automate that. We are a nation run by lawyers and bureaucrats.
From what I've heard, the self checkouts are cheaper for the store, even taking into account the theft that they've made possible.
UPC/barcode swapping has been going on for years. Ever run across a low price item that doesn't have a UPC sticker on it? The sticker probably ended up on a more expensive item. Just another reason why the inventory counts are off so often.