Another unusual aspect of our "billing policy" -- if we can call something so loosely negotiated as a "policy" -- is that we practically never charge any client an hourly rate above what he or she would themselves charge, if their work is suited to being hired out. It's a matter of respect for us, and stems from a sense that everyone is basically equal, whatever career they may have chosen out of interest, a wish to help others, whatever. I know I am probably wrong as hell about this on some rare occasion, but I would like to think that no one has chosen their career path strictly on the basis of money.
Another thing to mention here is the fact that we are totally open about the negotiating process and strive to make ABSOLUTELY CLEAR that the creative process is not like buying flour or cheese or sugar, by the pound or kilogram. It is extremely difficult to establish a perimeter on projects which grow, mutate, fly or occasionally, crash outright, and put a fixed price on such things. Those of us having created or built anything know very well that sometimes "the stars line up" and sometimes they don't, and pricing can be difficult. For this reason, many creative folks are pretty sloppy with billing, often putting off doing actual invoicing, until the time when things get tight and they can see straight through to the back of the fridge without obstacles. Not good.
Our accounting process isn't quite that reckless but some sweet clients have been known to ask "Hey, it's been months since you sent us an invoice, please, let's do something about that, or we'll feel shy about sending more work, for fear you aren't going to earn anything anyway..." Which in essence is a nice way to hear that those darling folks, really, want me also to make ends meet. As a result, we gladly do a rush project for them now and then, or work on a weekend.