Big bakery company adverts for a “Sale or Return” bun.

Well…

What’s the difference between a bun and an industrial eatable bun-like object?

Bun:
You can sell it because it’s a good product. That normally means you invest time, care and good basic materials to make the bun a good one. The customers like it and therefore buy it.

Industrial eatable bun-like object:
You only put as much material and time and effort into the production of a bun as necessary. So to say… as long as you still can call it a ‘bun’ (depending on local food laws) you can sell it. And you use your time and care to do a lot of advertisement.