Here are some things that are in demand by unethical traders ...
The 'Free End' papers of old books:
Many antiquarian books had blank pages bound in at the ends of them - these are called free end papers.
So have you ever wondered why people buy, very old and dull Latin texts from the 17th and 18th centuries? ... well they might not care about the book, but if you slice out the blank sheets of paper you have genuine original paper that is three or four hundred years old.
Who cares? Well perhaps an unscrupulous person might do a drawing on one of these sheets of paper and if they are skilled then ... well you can guess the rest.