So it is expected for the companies to specialize towards one type of product, so that is why there is only one price. One potential issue is someone could buy some low quality product and change into a high quality retail store. This could cause the low quality items to get stuck in the players inventory, taking up precious inventory space.
The only way to get rid of it is to let all the high quality items to run out, and then sell the low items off till the store becomes empty. This could be costly to miss out on days of selling the high quality items, it might be cheaper for the business to just dump the lower quality items altogether.
Maybe a small dumping fee could be added. Having the ability to dump all items below a certain feature or quality rating could be a very nice feature.
Note: An are you sure pop up may be nescessary to prevent unwanted dumpings.