The law is not as unprepared as you seem to think.
The law in most countries, including Germany, is very clear: if you're going to sell your products or services to individuals and businesses in those countries, you become subject to the laws applicable to that type of transaction in those countries.
If you don't want to be subject to German law, don't sell products or services to people in Germany.
Yep, the law is ruthless. However, for compliance reasons just checking the IP and the payment method is probably enough (definitely check that with a lawyer and a tax advisor; IANAL).