Michael Stiller is a Steuerberater (German certified tax advisor) and Expert-Comptable, registered with the Steuerberaterkammer Rheinland-Pfalz, the regional chamber of tax advisors. At Vaytax (vaytax.com), he reviews and files German VAT returns for online sellers based outside Germany.
The German statutes cited here (UStG, AO) are published in full at gesetze-im-internet.de, and the EU VAT Directive at eur-lex.europa.eu.