creating nodes with many to many relationship type with some fields?
You are looking for the capabilities in the Relation module. With it you can relate a seller to a book, and attach a price field to the relationship. 


  Relation is an API module and storage model for both simple and the
  most complex relations between entities. The module can handle both
  directional and symmetrical relations very well.
  
  Relations are entities and can therefore have fields. This makes
  Relation the most flexible and powerful relation model out there.
  (Still, using Relation with anything but the default SQL storage will
  not work in most cases.)