Even if they accurately charged shelf prices, these places are still a ripoff targeting the vulnerable. The list price is low but the per-unit price is astronomical compared to grocery store prices.
Have you ever been to a dollar store? Its much cheaper for the same items than a regular grocery store. Also not everyone needs a Costco sized tub of mayo. You test it yourself go by a standard sized candy bar at safeway/alberstons and then at a dollar store. Bottle of coke. Birthday card. Better yet compare the cost spices. Try to buy bay leaves at regular grocery store for under $5.