In all seriousness, the one question I could never answer for myself is "what happens when there's cocaine in the box?" Have you considered this and how this risk will be handled?
Reminds me of the Mitch Hedberg joke: "I love my FedEx guy cause he's a drug dealer and he doesn't even know it...and he's always on time."
As a market place ensuring safety is the value add. Having a rating system would be nice. Perhaps requiring only facebook/linkedin could help?
Or drivers upload their photo and drivers license and the photos should match? I don't have a solution, but something to think about.