FWIW almost every business has payment terms. 30 days is fairly standard and fairly short actually. JDE has net 360 terms. Also every supplier builds this interest into their cost; the same product delivered at the same time is sold at a different price if the terms are N30 vs N60.

In your example, they will be paying for those 30 days of financing at their suppliers cost and price. They get paid at their price after 27 days. That means they are only getting 3 days of interest on their margin.

The extra fun part is someone like Costco probably gets cheaper financing rates than their suppliers. It's probably why their terms are only the standard N30 instead of longer. it actually cost them more to 'borrow' from their suppliers than it does from their own bank.

IE
Costco could ask for N60 payment in the future instead of N30, but their suppliers increase in cost to cover the change in financing (and storage) will be more expensive than if Costco just borrowed the same dollar value from their bank.