DXB,
Please define "regular" in the interpretation of German law.
In my experience of working with contractors some 90% of them remained domicile in their home countries and commuted to/from their contracted place of work.
I'm a hotelier, occasionally the cops come asking for guest information, data privacy laws prevent me from providing it, you're suggesting that all German hotels/guest houses etc. shall provide such illegal information and that it is a taxable offence to take a holiday in Germany?
To repeat myself ... I'm recognising an envy from individual(s) that have been compelled to pay tax/SS against those that have managed to escape paying it.