WalMart is a first-tier store?
Yeah, if you visit America, go to a Sav-a-Lot or a Dollar General, and you'll see what they mean.
Walmarts, even the lousy ones, carry a heavy selection of name brand products. Walmarts are also mainly differentiated in their "experience" by the clientele and the workers, since the buildings and facilities are all pretty much even in terms of construction etc. within a few years of each other, or the last remodel.
There are Walmarts in upscale suburban areas that are actually pleasant to shop in, because many of the employees are drawn from that area, and most of the customers are too. These stores are often "as nice as a Target."
The Sav-a-Lots and Dollar Generals, they occupy a space between Walmart and the $.99 cent stores, operate out of older leased retail spaces of various shapes and sizes, and all tend to have a sad poverty-stricken edge to them. And are filled with lower quality generic off-brand merchandise. Name brand products are usually surplus overstock that failed to sell at higher tier retailers.