I once did some consultancy for a beverage company owned by one of the listed companies in the NSE.
Those guys told me that despite their big name and assumed connections, they couldn't squeeze better payment terms than 60 days AFTER SALE of items from supermarkets (Note: not after delivery to supermarkets but after the supermarket sells the product!).
That there is the precise reason why I don't understand how Nakumatt biz went down not unless the owners wanted it to.
If he has capital, he can try and push. Try hire a good sales person to talk supermarket chains into allowing him to sell in their stores. But he'll need the capital because for a starter they will insist on consignment model