Sure, this is the 'contractor' approach where you bill for services provided at a higher rate than a pure salary, and pay for your vacations/sicknesses/whatever out of that.
As for that "Scheinselbstständigkeit", I believe most other countries have some similar legislation. It's not an issue with freelancers as you have rotating clients, even if it's only one at a time; but yes, if you're creating it just for a single employment then that can be treated as tax avoidance - having the employer run a shell-subsidiary-branch would be preferred in that case.
As for that "Scheinselbstständigkeit", I believe most other countries have some similar legislation. It's not an issue with freelancers as you have rotating clients, even if it's only one at a time; but yes, if you're creating it just for a single employment then that can be treated as tax avoidance - having the employer run a shell-subsidiary-branch would be preferred in that case.