creating nodes with many to many relationship type with some fields? This is in line with How to structure a &quot;many-to-many&quot; relationship between nodes. 

To keep things in line with the example from the linked thread, what if i was a book warehouse and i had a list of all my books but i want to allow each seller to name his own price and show that book in the seller's store view with only the price that he set?

How would I allow him to edit the info of his entry without having access to anyone else's entry? I am trying to avoid associating nodes from different content types like creating a node type seller's price and reference a book inside of it.

I thought about a combination of field collection, content access, and TAC to try to make each seller capable of entering and editing their own price field collection. While I thought that field collection would create a new collection for every user, this doesn't seem to work: All sellers end up editing the same collection.

Do you have any idea?
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.)