[niggler]

FTA, Amazon's core business is "build[ing] a massive online database and offline infrastructure to transport boxes from warehouses to hundreds of millions of doorsteps", and I would argue that Costco's physical presence, existing warehouse efficiency, and brand identity positions them well for a foray into Amazon's business.

As for "offer something better other than price", most people point to customer service, and in my experience Costco's customer service completely blows away Amazon.