A term originated by one Mr FandL describing wankers who list a few books on Ebay, Amazon or Abebooks. By doing this they perceive that they suddenly have the status of Maggs Brothers.
An upper middle class housewife from Kent lists her husband's library of law books on abebooks for £1.00 each and tells all her friends that she is an antiquarian bookseller. When husband finds his rare and valuable collection on the shelves of Maggs brothers the wife is found strangled on the side of the road. An example of what happens to a vanity seller.