I often buy groceries and household chemicals from Walmart, it's convenient, especially when you order online and just drive up to pick it up. But once I received the wrong product, and returning it turned out to be not so easy. Later on https://walmart.pissedconsumer.com/customer-service.html I read that many people face such confusion. Now I always double-check the order before paying.
RE: Small Vs Big (in supermarkets)