Not to mention the effect of neighborhood re: nearby shopping options. I've lived in very poor and fairly rich neighborhoods, and the difference in quality of local grocery stores is dramatic. There are chains I didn't realize even existed, because they targeted different class neighborhoods. And even within a chain, the level of effort put into a given franchise location can vary pretty dramatically as well.

And that's in the states. In the UK, it's a running joke that the different supermarket chains are subdivided along class lines.