Maybe I'm wrong, but I think they've changed their front page over the course of the day (perhaps in response to these comments).

When I first read it, it looked like a way for advertisers to reach potential buyers. If that's the case, then someone on oDesk could easily respond pretending to be interested in a product just as well as I could.

Envisioned more broadly as a way to pay for the time someone spends responding to email, it would be hard to outsource my role in email correspondance.