All retailers pay the same price on thier products. And its the wholesale price. They buy thier products from distributers. The distrbuters are authorized by the manufacturers and actually pick up the products from the plants and distribute them to the retailers.
there is no massive profit margins.
The only way you can profit well is if you sell at retail. This is where many ebay sellers go wrong. They believe that the wholesale price must be lower then what ebays average selling prices are. But most dont understand that many items sell for below wholesale.
If a retailer or a distributer has an overstock of an item they will drop the prices below thier purchasing cost to clear then out and recover some lost investment profits. But for a retailer that sells billions of items a year its not a huge loss. And is just considered business as usuall. For a small business or internet seller this can completely destroy thier company.
Places like walmart and thier falling prices scheme beats out thier competition. Its possible half the profit potential on many items but since they sell massive volume it still keeps them on top.
Have you never seen the documentary on walmart ? Walmart forces distributers to provide a lot of items at a certain price otherwise they will not allow them to sell the products through the walmart chain.