Unregistered client have to insert email too - Where will the shop send an order confirmation? - by post to the address? It kind of doesn't make sense, does it?
Why do you trust customers? I have experience that they are not telling the truth and trying to deceive the administrators (and they are not only customers from the Czech Republic, but also Germany, Slovakia, Poland, Hungary, Austria, Russia, Ukraine, France, Italy, ...) I am often disgusted with them