Proximity to pain
The closer you are to the point of need, the more you can charge.
Pizza at the airport costs five times more than pizza on the way to the airport.
Tax audit services in the middle of an SEC investigation cost triple what they cost before one.
Scalped tickets cost more than ones bought in advance, by mail.
Emergency towing in a strange town costs more too.
The single easiest way to increase your fees is to get closer to the pain. It's interesting to note that no large-scale advertising ventures are closer to the pain than the Yellow Pages or Google. Both of which are insanely successful.