I think the real problem here is that Walmart are trying to overprice people and then console them with the offer that if they can bring in a cheaper price they will honor it. The real solution would be Walmart not overpricing, but clearly they are not prepared to do that so they offer these deals.
These deals trick consumers into thinking that they will obviously get the best deal there as why else would the shop offer this deal. The cashier does not necessarily know how much these items are worth and it is clearly not their fault. It is a large company trying to extort as much money as possible from the people who do not bother. If they are not willing to put in price checks with other shops and keep wanting to overcharge normal customers, then this is the way they must do business.