But often there's a special rule when you work in the company in question, in which case you have to pay income tax on a certain fraction of dividends, with something similar for the sale of the company.
Yes, but in order to prevent people from bypassing the rules similar rules almost always apply to sales. It's a system made to ensure that income from work is taxed as work, whether you extract the money by dividends or through a sale.
For example, in Sweden we have a set of rules called 3:12 rules, which govern people who simultaneously own parts of a company and also work in it. In Sweden we have an exemption for large sums, for which ordinary capital taxation rules are applied, and the German law is very similar, only with a much higher exemption.
