Sorry I'm late to this question. I wanted to answer this: "How do bootstrapped startups handle huge companies like Zappos?" From my experience, big companies like working with small vendors because they can push them around. That may sound negative but the larger company can ask for features and the small company will be happy to oblige. That is what I have seen and heard in my own time.

Also in my experience it has been a waste of time to think about scaling. Big companies do not simply look at your website and tell the lackey engineer to integrate your product into their production product and pray for it to work. There are going to be many phases of adoption which your ability to scale will be tested.

Scaling is a nice problem to have, worry about making something people want first.