Walmart uses their market size to force suppliers to produce special packaging for Walmart that is a slightly different sized box for many food items, where tha

Walmart uses their market size to force suppliers to produce special packaging for Walmart that is a slightly different sized box for many food items, where that product is a bit lighter than the same sized box at another retailer. The catch is Walmart advertises their price, which looks lower in print, but if one purchases that product at Walmart and also at another grocer you will find the Walmart version is slightly more expensive by weight, holds less than the other same sized box but labeled with the correct weight. Only a careful consumer will notice that Walmart costs more, if calculated by weight.