Ask yourself why the stores that charges 30% more are still around? Likely they operate in different areas, or they offer some services the cheaper place doesn't, or they have higher quality wares etc. Otherwise everyone would go shop at the cheaper store.

Now ask yourself, why doesn't the cheaper store offer those things? Maybe because they costs something?

>How can grocery store have a 1% to 2% profit margin, when the price of the same item across grocery store chains can vary by 10-30% or more?

1. Individual price discrepancies of "10-30% or more" doesn't really matter. What does matter is overall markups.

2. The stores themselves might be upscale/higher tier, which also makes their stuff more expensive. I'm not talking about whole foods carrying organic products, I'm talking about stores that have better selection, full service butcher/deli, better cleaning, better interior design/decoration, or better location (richer neighborhood).

>I can't imagine it coming down to a store having higher costs alone.

Your other option is assuming there is industry wide financial reporting fraud across multiple businesses and multiple countries for many decades.

Stores have different costs due to selling:

1) different quality of goods

2) employing different quality/quantity of workers

3) different locations having different real estate/insurance/tax/labor costs

4) offering fewer or more services/products

Etc.