“In his analysis of goodwill Scruton LJ in Whiteman Smith Motor Co v. Chaplin likened the analysis of a client base to the “cat, rat and dog”. The cat prefers the old home to the person, the dog represents that part of the client who follows the person rather than the place, and the rat follows neither and drinks elsewhere. Arguably there is a further creature which should be added to the managerie, the donkey, which is the practitioner, or the advisor, who simply believes that the value of goodwill can be determined by a rule of thumb.
A professional service firm is a business, and its value should be subject to the same criteria as those which apply to other commercial undertakings.”
Wayne Lonergan “The Valuation of Businesses, Shares and Other Equity”