Rohan says a big supermarket will always be cheaper than a small kirana shop, because it is big

Why

Rohan has half the picture right: a big supermarket buys in huge quantities, which lets it pay the wholesaler less per item and pass some of that saving on. But size also brings big costs — a large rented space, many staff, lighting and air-conditioning, and prices often set for a particular kind of customer. A small kirana shop has low overheads, buys from a nearby wholesale market, and the owner works the counter themselves, so on everyday items — atta, dal, oil, soap — it can match or beat the supermarket. Test it: compare the price of a few basic staples at both — often they are within a rupee or two, and the small shop wins on some, because its lower running costs cancel out the supermarket's bulk-buying edge. His sister is right: being big helps with buying power but does not guarantee the lowest price — a small shop's low costs can even it out.