There can be no substitute for applying rational, justifiable valuation criteria to the valuation of any business. Following this, one stands back and considers whether the result is reasonable, is it consistent with the market place. Sometimes with the industry benchmarks one will then acknowledge that the market will pay more or less based on known practices. If one can be confident that the market will accept the benchmark, or “Rule of thumb” value then at the end of the day that may well be the value”

A R Burn “Practical Small Business Valuations”