What eg. a German (very!) rich person would do is get a second passport in Cyprus and then open a Swiss bank account. To the Swiss bank, they'd say that they only have that one passport from Cyprus. Therefore, the Swiss bank does not report to the German state that the German individual has a bank account. This is how that person avoids German tax.
0. https://www.kuechenstud.io/medienradio/podcast/di090-geldwae...
also how does having a large bank account in swiss affects her taxes in germany?
If a country sells its citizenships, that country alone benefits financially from that transaction, but the potential obligations are borne by the entire EU community.
In my opinion, there is nothing inherently wrong about a country selling its citizenship, but in the EU framework it seems to go against the good faith principles that the EU is built on.