They don't have no margin (i.e. nothing is 'at cost' as GP presumes), they just have very low margins which they make up for with high volume.

It's not that novel, but Bezos has created a company with tolerance for lower margins.

> Huh? So how does Amazon actually make money?

They sell at/near their cost (including warehousing, delivery, technology, etc.) which is lower than the cost of Walmart's brick and mortar presence.

Costco also sells at cost, almost all their profit is from membership fees (see Amazon Prime for Amazon's take on this.)

When did they start making money, again?

They have posted a profit the last 8 quarters.