Very good points. I was thinking about the trust issue and it is tricky. Incentive for fencing the item(s) must be lower than incentive for delivery. Things like this comes to mind: http://news.ycombinator.com/item?id=1848278

Might have to cap the cost of the items you can deliver to something like £200

Also if you knew what driver last had the package, and it was never delivered, then some sort of punishment happens. Works in theory but there is lots I am probably not thinking of :)