Comment by TomK32

I've read a few of those articles in recent months, both in English and German, and I did read any book title that was rare. The Rare Book & Special Collection Div at the Library Congress considers books published before 1801 as rare. Searching for old books on abebooks is surprisingly hard but I didn't find any for less than 10 Euro and nothing in those articles suggested they were buying up anything but cheap books.