Short update on that VAT added-eBay-case:
My money is back!
The selling company wrote that they indeed put on their offers on eBay.com where there's no VAT-regulation like for the EU eBay-sites/-companies. They also wrote that they think that putting their terms and conditions is enough even if they offer an item on eBay.com and e.g. eBay.de with their conflicting terms and conditions.
In the end they agreed to the points I made and cancelled the order apologizing for causing trouble on my side.
I think a reliable seller over all.
As a private customer I won't buy from them because their prices are too high after adding 24% VAT to price and shipping..