Yeah... I used to work in one of those places. Even though the shop is doing the customer a favour by selling them stuff so cheap, they still want everything cheaper and cheaper.
Also, the part about the shops selling 'the same products' is not true, because I know for a fact that 99p Stores has its own line of products which only they can sell. Unless an independent trader were to buy shitloads of products from them and sell them on a market stall with increased prices (this actually happens), but a real 'shop' wouldn't do that just to make a penny on each item. Not worth it.
But as I was saying, the fact that people went there just to save a penny is very characteristic of the people who do a lot of shopping in those places. You get people bringing brand-named products (which cost over three times as much in the supermarkets) to the counter, and claiming it was in the 50p clearance section. Pathetic.