[krav]

eBay's a middleman. So's Google (for information). Being a middleman is fine - just add some value and efficiency in the process.

[dtap]

I don't think you need to add anything. As you get better at matching buyers and sellers you get closer to equilibrium and make everyone happier.

[dzlobin]

Except the company who tried to kill Octopart( see pg's startup school 08 talk.)