The commercial troubles of 1816 brought into difficulties the banking house with which he was connected, and forced the sale of his collection of books and pictures. Dr S.H. Spiker, the king of Prussia's librarian, visited Roscoe at this difficult time. Roscoe said he still desired to write a biography of Erasmus but lacked both leisure and youth. The project was never carried out. Around this time Roscoe was asked to investigate the claims of the blind girl Margaret M'Avoy, who was said to be able to read using her fingers, at the request of Sir Joseph Banks. Roscoe concluded that her amazing abilities were due to the fact that she was not blind.