Buyer only bought this book to be able to send an expensive cease-and-desist warning letter. We forgot to set the new price for the book and in Germany there are fixed book prices. People without a conscience are allowed to ruin small booksellers using cease-and-desist warning letters, even if the book was sold for a higher price including shipping cost.
Sold for 10,00 € + 2,50 €, fixed price was changed to 11,00 € before. For that small discrepancy of 1 Euro they wanted over 1000 Euro.
In Germany, this bad practice is possible as it is allowed to charge for these letters, even if they are sent because of 1-Euro trifles.