I think this question is a very important one, especially when you are considering a business valuator, but at other times as well.
I don’t know about other jurisdictions, but in Canada, the Canadian Institute of Chartered Business Valuators specifies different levels of business valuation advice. They have rules as to how much background work and documentation that needs to be done to render a calculation of business value, an estimate of business value, and a comprehensive opinion of business value. Each requires an escalated amount of work to be done by the valuator.
My view is, and has always been, that if someone is going to give business valuation advice irrespective of what they call that advice, they need to focus on the likelihood that those seeking the advice are likely to place reliance on it. So my view is that, irrespective of how those giving business valuation give calculations, estimates, or so-called comprehensive opinions need to express their conclusions to the people who get the advice and need to remember the number. So while I might in some instances given a litigating party and his/her lawyer a verbal view on possible value outcome, I never myself ever gave written valuation calculations or estimates. I have only ever given opinions because my bottom line is that the recipient of written valuation calculation or estimate is going to place pretty much the same weight on that as they will a written opinion - or if they don’t, they might. So I believe that rendering written opinions is the right way to do it.
Having said that, I’m a great believer in the 80-20 rule when it comes to valuations. I believe you can get to most of the answer unless some exceptional things come out that you’re not expecting with about 20% of the work, and that the a great deal of time is spent in documenting and writing a report.
I also believe that if you do valuations every year or every second year for a group of business owners that the time taken to do subsequent valuations should not be nearly as much as the time it takes to do it in the first year. Finally I believe that if the right valuators are chosen to generate opinions the business advice they might give their client may prove to be more valuable to the client than the business valuation fees they are charged. So if the valuator goes outside their scope of what they are being asked to do and says, "Look, you should also ask me what I think of how you might be able to grow this business. I know your business reasonably well from other work I’ve done. Here are my views as to what you might do to improve your growth potential", that can prove to be a very valuable sidebar service.