A mandate is a serious matter in Germany. The client needs to think through and research carefully, which service providers are not only capable, but more importantly trustworthy.
Even though German law strictly defines the relationship between for example an attorney or tax advisor and the client, the German client seeks a kind of special relationship over the long term, similar to one between a physician and a patient. For the German client its a matter of discretion.
And even when the advisor has significant decision making latitude, there is nonetheless constant dialogue and collaboration between the two parties. This is more than a typical business relationship. It is both business and personal. It is about representing the interests of the client in complex matters.
Both parties need to respect each other at a deeper level. They must be convinced that they can work together. Any kind of misunderstanding can lead to a difference of opinions, which potentially can allow mistrust to seep into the working relationship.
A political mandate is different. Although the office holder focuses on serving the interests of the voters, there is no personal relationship between them. The voters have to demand transparency in order to fully trust their elected office holder.
And because office holders have to represent the interests of many kinds of voters, there is a certain natural level of mistrust over and against her or him. If voters are dissatisfied, or have lost trust in the office holder, the political system enables them to end the relationship.
Taking on a mandate is a complex and delicate matter in Germany. In business as well as in politics.