I recently returned from a vacation to Oregon and stopped (as has become a ritual, or at least a habit) to buy some local honey from an honor box on Route 99W in Dundee, Oregon.
The amazing thing about this “store” is that: I know exactly what’s there and where to find it; I don’t need a salesperson to help me out; and the store owner trusts me to pay the right amount of money even while unattended. And … it works. The stand has very low overhead, I keep getting honey and (presumably) the economics of it work.
This illustrates a great tenet of user experience and usability research: if users can do what they need to do without you there, you’re probably doing a good job. If they need you to explain what to do, try to make it simpler and you’ll get more customers (or at least well-trained ones.)