"Flat Rate" is the practice of giving the customer, in advance, a firm price for the job. Simply put, you just say "I'll do it for $123." When the job is done, you expect a check to be ready.
Some folks put together "price books." These are the results of experience, and condense routine jobs into a form that can be consulted, and provided to everyone in the fleet. The advantage is speed and consistancy.
How you arrive at your price is another matter entirely.
