In 1804-05 printer and bookseller Martin Sylvestre Boulard wrote, printed, and published the first practical manual for antiquarian booksellers, entitled Traité élementaire de bibliographie, contenant la manière de faire les inventaires, les Prisées, les Ventes Publiques et de classer les Catalogues. Les bases d'une bonne Bibliothèque et la manière d'apprécier les livres rares et précieux. Ouvrage utile à tous les bibliographes et particulièrement aux Bibliothècaires et aux Libraires qui commencent in Paris in An XIII of the French revolutionary calendar (1804-05).
Having read parts of this 140-page work online, it is clear that not only was Boulard a printer and a seller of his own books, but he was also a dealer in rare and out of print books. In this work Boulard approached the subject matter both from the bibliographic and economic points of view. He stated many of the principles of the trade that applied in his own time, and may be extrapolated to the trade today. Of course, collectors' taste was very different between then and now, and most significantly, the French Revolution caused an immense redistribution of antiquarian books and manuscripts of all kinds, through the closure of monasteries, the merging of institutions, and the sale of the libraries of certain members of the ancien regime. By the time Boulard published his book the opportunities for collecting rarities must have been absolutely unprecedented in the history of the book trade up to his time. Books and manuscripts thrown onto the market during the French Revolution supplied the antiquarian book trade, directly and indirectly, well into the mid-19th century.
Janssen, "The Oldest Practical Manual for the Antiquarian Bookseller," Bulletin du Bibliophile (1997) 367-74.