The item's location, a German-language description and domestic postage rates prove nothing about authenticity. As early as the mid-2000s there were sellers with German addresses sourcing their goods directly from Far Eastern counterfeiting workshops, using sober, unremarkable listing text that read as perfectly accurate. The conspicuous listings shipped straight from China were already in decline by then, because they were too easy to see through.
One useful indicator is where the pictures come from. If the product photographs are hosted not on the trading platform itself but on a third-party server, the image address in the page source will show it; where that address points to a foreign wholesaler, the goods very probably come from there too. It is equally telling if the same photograph turns up in numerous other listings, since that means it is catalogue material rather than the pen actually being sold. Reputable sellers photograph the individual pen themselves, show the nib, clip and cap rings in close-up, and answer detailed questions without evasion.