The principle underlying appraiser standards is that value conclusions should be recognized as generally correct by any member of the business valuation community. Or, conversely, any member of the valuation community should conclude a generally similar value for the same business. So, professional standard business valuations are not simply someone's opinion. They are the opinion of a community of professionals who have the requisite educational knowledge and experience to render such an opinion.
The following links will help you understand the skills needed to perform a valuation, the varied requirements of the appraiser credentialing organizations, and standard appraiser rules and ethics.