Looking at the original bookshelf module, I think it would be useful to add a parameter function that would make the Amazon reference/interface an option, rather than a default setting. I have plenty of books I would like to feature and advise to my users, without a desire to sell them via Amazon. There are plenty of other sources around the world that offer on-line book sales.
My sugestion would be:
- ISBN number only as reference, no link to sales mechanism.
- Create aditional field where users can optionaly add their prefered on-line bookseller, i.e the URL of their affiliate programm.
Cheers
Ben